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1

Nonlinear traveling waves in confined ferrofluids.

We study the development of nonlinear traveling waves on the interface separating two viscous fluids flowing in parallel in a vertical Hele-Shaw cell. One of the fluids is a ferrofluid and a uniform magnetic field is applied in the plane of the cell, making an angle with the initially undisturbed interface. We employ a mode-coupling theory that predicts the possibility of controlling the speed of the waves by purely magnetic means. The influence of the tilted magnetic field on the waves shape profile and the establishment of stationary traveling wave structures are investigated. PMID:23214870

Lira, Sérgio A; Miranda, José A

2012-11-01

2

NSDL National Science Digital Library

This article from the University of Wisconsin is part of a series on nano topics devoted to ferrofluids. The article describes what ferrofluids are and discusses how they are produced, along with possible applications. There are also several images of ferrofluids being manipulated with magnets.

2010-01-15

3

Hydrodynamic theory of polydisperse chain-forming ferrofluids.

The larger magnetic particles in ferrofluids are known to form chains, causing the fluid to display non-Newtonian behavior. In this paper, a generalization of the familiar ferrofluid dynamics by Shliomis is shown capable of realistically accounting for these fluids. The modification consists of identifying the relaxing magnetization as that of the chain-forming particles, while accounting for the free magnetic particles by dissipative terms in the Maxwell equations. PMID:18351932

Mahle, Stefan; Ilg, Patrick; Liu, Mario

2008-01-01

4

Experimental and numerical investigation of wave ferrofluid convection

NASA Astrophysics Data System (ADS)

The stability of buoyancy-driven shear flow in an inclined layer of a ferrocolloid is investigated for different values of inclinations and homogeneous longitudinal magnetic fields. Near the onset of Rayleigh convection of ferrofluid layer inclined with respect to gravity, the wave oscillatory regimes were observed in experiments and numerical simulations. Visualization of convection patterns is provided by a temperature-sensitive liquid crystal film. As experiments testify, the origin of traveling wave regimes in ferrofluid is due to concentration gradients caused by gravity sedimentation of the magnetic particles. To study the effects of initial concentration gradient of particles, on convective instabilities, finite volume numerical simulations using a two-phase mixture model were carried out for the same setup. The most fascinating effect in ferrofluid convection is spontaneous formation of localized states, those where the convection chaotically focuses in confined regions and is absent in the remainder of cavity.

Bozhko, A. A.; Putin, G. F.; Tynjälä, T.; Sarkomaa, P.

2007-09-01

5

Experimental and numerical investigation of wave ferrofluid convection

The stability of buoyancy-driven shear flow in an inclined layer of a ferrocolloid is investigated for different values of inclinations and homogeneous longitudinal magnetic fields. Near the onset of Rayleigh convection of ferrofluid layer inclined with respect to gravity, the wave oscillatory regimes were observed in experiments and numerical simulations. Visualization of convection patterns is provided by a temperature-sensitive liquid

A. A. Bozhko; G. F. Putin; T. Tynjälä; P. Sarkomaa

2007-01-01

6

The dispersion of parametrically excited surface waves in viscous ferrofluids

NASA Astrophysics Data System (ADS)

Surface waves on a ferrofluid, which is exposed to a normal magnetic field, may exhibit a non-monotonous behavior. Stationary standing waves can be excited mechanically by a vertical vibration of the vessel, or magnetically by a modulation of the applied field. A linear stability analysis for the onset of these parametrically excited waves is presented. It will be shown that a careful choice of the filling depth allows for a detection of the anomalous dispersion branch. Furthermore, a theoretical confirmation is provided for the synchronous wave response, recently observed in a magnetic Faraday experiment.

Müller, Hanns Walter

1999-07-01

7

NASA Astrophysics Data System (ADS)

Suspensions of magnetic nanoparticles have received increasing interest in the biomedical field. While these ferrofluids are already used for magnetic resonance imaging, emerging research on cancer treatment focuses, for example, on employing the particles as drug carriers, or using them in magnetic hyperthermia to destroy diseased cells by heating of the particles. To enable safe and effective applications, an understanding of the flow behaviour of the ferrofluids is essential. Regarding the applications mentioned above, in which flow phenomena play an important role, viscosity under the influence of an external magnetic field is of special interest. In this respect, the magnetoviscous effect (MVE) leading to an increasing viscosity if an external magnetic field of a certain strength is applied, is well-known for singlecore ferrofluids used in the engineering context. In the biomedical context, multicore ferrofluids are preferred in order to avoid remanence magnetization and to enable a deposition of the particles by the organism without complications. This study focuses on a comparison of the MVE for three ferrofluids whose composition is identical except in relation to their hydrodynamic diameter and core composition—one of the fluids contains singlecore particles, while the other two feature multicore particles. This enables confident conclusions about the influence of those parameters on flow behaviour under the influence of a magnetic field. The strong effects found for two of the fluids should be taken into account, both in future investigations and in the potential use of such ferrofluids, as well as in manufacturing, in relation to the optimization of flow behaviour.

Nowak, J.; Wiekhorst, F.; Trahms, L.; Odenbach, S.

2014-04-01

8

Suspensions of magnetic nanoparticles have received increasing interest in the biomedical field. While these ferrofluids are already used for magnetic resonance imaging, emerging research on cancer treatment focuses, for example, on employing the particles as drug carriers, or using them in magnetic hyperthermia to destroy diseased cells by heating of the particles. To enable safe and effective applications, an understanding of the flow behaviour of the ferrofluids is essential. Regarding the applications mentioned above, in which flow phenomena play an important role, viscosity under the influence of an external magnetic field is of special interest. In this respect, the magnetoviscous effect (MVE) leading to an increasing viscosity if an external magnetic field of a certain strength is applied, is well-known for singlecore ferrofluids used in the engineering context. In the biomedical context, multicore ferrofluids are preferred in order to avoid remanence magnetization and to enable a deposition of the particles by the organism without complications. This study focuses on a comparison of the MVE for three ferrofluids whose composition is identical except in relation to their hydrodynamic diameter and core composition-one of the fluids contains singlecore particles, while the other two feature multicore particles. This enables confident conclusions about the influence of those parameters on flow behaviour under the influence of a magnetic field. The strong effects found for two of the fluids should be taken into account, both in future investigations and in the potential use of such ferrofluids, as well as in manufacturing, in relation to the optimization of flow behaviour. PMID:24721897

Nowak, J; Wiekhorst, F; Trahms, L; Odenbach, S

2014-04-30

9

Hydrodynamics of ocean wave-energy utilization

This book presents papers on wave energy converters. Topics considered include hydrodynamics, resonance, air turbines, buoys, physical and mathematical modeling, nonlinear damping, China's research on wave power, wave climate, site selection, wave forces, ship propulsion, wave energy absorption, phase control, optimal control, oscillating water columns, air flow, pneumatics, wave propagation, the survival of surface-piercing wave energy devices in extreme waves,

D. V. Evans; A. F. de O. Falcao

1985-01-01

10

Efficiency of magnetic plane wave pumping of a ferrofluid through a planar duct

NASA Astrophysics Data System (ADS)

The efficiency of ferrohydrodynamic pumping of a ferrofluid through a planar duct by means of a running magnetic plane wave is studied to second order in the amplitude of the exciting current density. The rate of dissipation in the fluid is calculated from the first order magnetic field and magnetization. It turns out that the efficiency, defined as the ratio of net flow velocity to power input, is comparable in magnitude to that for Stokes peristaltic pumping. The theory for electrohydrodynamic pumping of a polar liquid by means of a running electric plane wave is shown to be nearly identical.

Felderhof, B. U.

2011-09-01

11

NASA Technical Reports Server (NTRS)

A new Ferrofluidics exclusion seal promises improvement in controlling "fugitive emissions" -vapors that escape into the atmosphere from petroleum refining and chemical processing facilities. These are primarily volatile organic compounds, and their emissions are highly regulated by the EPA. The ferrofluid system consists of a primary mechanical seal working in tandem with a secondary seal. Ferrofluids are magnetic liquids - fluids in which microscopic metal particles have been suspended, allowing the liquid to be controlled by a magnetic force. The concept was developed in the early years of the Space program, but never used. Two Avco scientists, however, saw commercial potential in ferrofluids and formed a company. Among exclusion seal commercial applications are rotary feedthrough seals, hydrodynamic bearings and fluids for home and automotive loudspeakers. Ferrofluidics has subsidiaries throughout the world.

1993-01-01

12

Smooth Particle Hydrodynamics for Surf Zone Waves.

National Technical Information Service (NTIS)

Smoothed Particle Hydrodynamics (SPH) is a meshless numerical method that is being developed for the study of nearshore waves and other Navy needs. The Lagrangian nature of SPH allows the modeling of wave breaking, surf zones, ship waves, and wave-structu...

R. A. Dalrymple

2009-01-01

13

NASA Astrophysics Data System (ADS)

In this study, an optical scheme based on Stokes-Mueller Formalism and rotating-wave-plate Stokes polarimeter is successfully developed for obtaining concurrent measurements of the linear birefringence and dichroism. For a quarter-wave plate sample, the measured values of the principal axis angle and retardance are found to have average absolute and normalized errors of 0.0859° and 0.76%, respectively, while the measured dichroism of the quarter-wave plate has an average value of 0.0203. When analyzing ferrofluid film samples with concentrations ranging from 2 to 6%, it was found that for a given concentration of ferrofluid, retardance increases with applied magnetic fields and tends to saturate at high levels. Additionally, under the condition of the same magnetic field, the experimental results show that retardance is proportional to the concentration; the higher concentration will result in more retardance and absorption. Consequently, the derived algorithm for concurrent measurements of the linear birefringence and dichroism is feasible, and the relation between the concentration and magneto-optical effect was successfully investigated.

Lin, Jing-Fung; Lee, Meng-Zhe

2012-04-01

14

Strong dipolar effects in a quantum ferrofluid.

Symmetry-breaking interactions have a crucial role in many areas of physics, ranging from classical ferrofluids to superfluid (3)He and d-wave superconductivity. For superfluid quantum gases, a variety of new physical phenomena arising from the symmetry-breaking interaction between electric or magnetic dipoles are expected. Novel quantum phases in optical lattices, such as chequerboard or supersolid phases, are predicted for dipolar bosons. Dipolar interactions can also enrich considerably the physics of quantum gases with internal degrees of freedom. Arrays of dipolar particles could be used for efficient quantum information processing. Here we report the realization of a chromium Bose-Einstein condensate with strong dipolar interactions. By using a Feshbach resonance, we reduce the usual isotropic contact interaction, such that the anisotropic magnetic dipole-dipole interaction between 52Cr atoms becomes comparable in strength. This induces a change of the aspect ratio of the atom cloud; for strong dipolar interactions, the inversion of ellipticity during expansion (the usual 'smoking gun' evidence for a Bose-Einstein condensate) can be suppressed. These effects are accounted for by taking into account the dipolar interaction in the superfluid hydrodynamic equations governing the dynamics of the gas, in the same way as classical ferrofluids can be described by including dipolar terms in the classical hydrodynamic equations. Our results are a first step in the exploration of the unique properties of quantum ferrofluids. PMID:17687319

Lahaye, Thierry; Koch, Tobias; Fröhlich, Bernd; Fattori, Marco; Metz, Jonas; Griesmaier, Axel; Giovanazzi, Stefano; Pfau, Tilman

2007-08-01

15

NSDL National Science Digital Library

This page from the University of Wisconsin-Madison Materials Research Science and Engineering Center Interdisciplinary Education Group offers seven videos that show ferrofluid behavior in a magnetic field. QuickTime is required to view the videos.

2011-11-09

16

NASA Astrophysics Data System (ADS)

This issue of Journal of Physics: Condensed Matter is dedicated to results in the field of ferrofluid research. Ferrofluids—suspensions of magnetic nanoparticles—exhibit as a specific feature the magnetic control of their physical parameters and of flows appearing in such fluids. This magnetic control can be achieved by means of moderate magnetic fields with a strength of the order of 10 mT. This sort of magnetic control also enables the design of a wide variety of technical applications such as the use of the magnetic forces for basic research in fluid dynamics. The overall field of ferrofluid research is already about 40 years old. Starting with the first patent on the synthesis of magnetic nanoparticle suspensions by S Papell in 1964, a vivid field of research activities has been established. Looking at the long time in which ferrofluids have been the focus of scientific interest, one can ask the question, what kind of recent developments justify a special issue of a scientific journal? New developments in a field, which depends strongly on a certain material class and which opens research possibilities in different scientific fields will nowadays usually require an interdisciplinary approach. This kind of approach starting from the synthesis of magnetic suspensions, including research concerning their basic properties and flow behaviour and focusing on new applications has been the core of a special research programme funded by the Deutsche Forschungsgemeinschaft (DFG) over the past 6 years. Within this programme—entitled `Colloidal Magnetic Fluids: Basics, Synthesis and Applications of New Ferrofluids'—more than 30 different research groups have been coordinated to achieve new results in various fields related to ferrofluid research. The basic approach of the program has been the assumption that new applications well beyond the typical ferrofluid techniques, for example loud speaker cooling or sealing of rotary shafts, will require tailored magnetic suspensions with properties clearly focused towards the need of the application. While such tailoring of fluids to certain well defined properties sounds like a straightforward approach one has to face the fact that it requires a clear definition of the required properties. This definition itself has to be based on a fundamental physical knowledge of the processes determining certain magnetically controlled phenomena in ferrofluids. To make this point concrete one can look into the detailed aims of the mentioned research program. The application areas identified for the future development of research and application of suspensions of magnetic nanoparticles have been on the one hand the biomedical application—especially with respect to cancer treatment—and on the other hand the use of magnetically controlled rheological properties of ferrofluids for new active technical devices. Both directions require, as mentioned, as a basis for success the synthesis of new ferrofluids with dedicated properties. While the medical applications have to rely on biocompatibility as well as on stability of the suspensions in a biomedical environment, the use of ferrofluids in technical devices employing their magnetically controlled rheological properties will depend on an enhancement of the changes of the fluid's viscous properties in the presence of moderate magnetic fields. For both requirements ferrofluids with a make up clearly different from the usual magnetite based fluids have to be synthesized. The question of how the detailed microscopic make up of the fluids would have to look has to be answered on the basis of basic research results defining the physics background of the respective phenomena. Taking these aspects together it becomes obvious that the aforementioned research program had goals aiming far beyond the state of the art of classical ferrofluid research. These goals as well as the basic strategy to achieve them is in a way reflected by the structure of this issue of Journal of Physics: Condensed Matter. The issue contains results emerging from the research pr

Odenbach, Professor Stefan

2006-09-01

17

Surface Instabilities of Ferrofluids

We report on recent progress in understanding the formation of surface protuberances on a planar layer of ferrofluid in a\\u000a magnetic field oriented normally to the surface. This normal field or Rosensweig instability can be tackled by a linear and\\u000a a nonlinear description. In the linear regime of small amplitudes we focus on the wave number of maximal growth, its

R. Richter; A. Lange

18

National Technical Information Service (NTIS)

The concept of using a ferrobluid rotating under the influence of an electromagnetic field as a gyroscope is reported. A ferrofluid is a colloidal suspension of ferromagnetic particles and behaves as a magnetic liquid. It was shown that up to about 100 dy...

G. Miskolczy R. Litte

1971-01-01

19

National Technical Information Service (NTIS)

An underwater sound generator composed of a ferrofluid contained within a toroidal container which has a rigid bottom and top and elastic cylindrical side walls. A coil of wire links the toroidal container and is adapted to be connected to a dc bias sourc...

P. S. Dubbelday R. W. Timme

1980-01-01

20

Traveling wave solutions for a quantum hydrodynamic model

A traveling wave analysis for a quantum hydrodynamic model is performed. The isobaric, isentropic, and isothermal cases are studied. In all three cases, the qualitative behaviour of the solutions is analysed.

Ingenuin Gasser

2001-01-01

21

Barium hexaferrite ferrofluids - preparation and physical properties

NASA Astrophysics Data System (ADS)

Barium hexaferrite BaFe 12-2 xTi xCo xO 19 ferrofluids have been prepared for the first time using oleic acid as surfactant and Isopar M ® as carrier liquid. The initial susceptibility versus temperature for zero-field cooling of the ferrofluid was obtained by a vibrating sample magnetometer. TEM pictures of the fluid show isolated particles and only small agglomerates and a mean particle diameter of approx. 8 nm. Numerical calculations of the magneto-viscous effect, based on the local-equilibrium magnetic state model, clearly show the benefit for Ba-ferrite ferrofluids resulting from the high uniaxial anisotropy compared to magnetite ferrofluids. Rheological measurements were performed with a rotational-type viscometer with magnetic field perpendicular to the hydrodynamic vortex axis.

Müller, R.; Hiergeist, R.; Steinmetz, H.; Ayoub, N.; Fujisaki, M.; Schüppel, W.

1999-07-01

22

Nonlinear Generalized Hydrodynamic Wave Equations in Strongly Coupled Dusty Plasmas

A set of nonlinear equations for the study of low frequency waves in a strongly coupled dusty plasma medium is derived using the phenomenological generalized hydrodynamic (GH) model and is used to study the modulational stability of dust acoustic waves to parallel perturbations. Dust compressibility contributions arising from strong Coulomb coupling effects are found to introduce significant modifications in the threshold and range of the instability domain.

Veeresha, B. M.; Sen, A.; Kaw, P. K. [Institute for Plasma Research, Bhat, Gandhinagar-382428 (India)

2008-09-07

23

Hydrodynamic waves and correlation functions in dusty plasmas

A hydrodynamic description of strongly coupled dusty plasmas is given when physical quantities vary slowly in space and time and the system can be assumed to be in local thermodynamic equilibrium. The linear waves in such a system are analyzed. In particular, a dispersion equation is derived for low-frequency dust acoustic waves, including collisional damping effects, and compared with experimental results. The linear response of the system is calculated from the fluctuation-dissipation theorem and the hydrodynamic equations. The requirement that these two calculations coincide constrains the particle correlation function for slowly varying perturbations. It is shown that in the presence of weakly damped, long-wavelength dust-acoustic waves, the dust autocorrelation function is of the Debye{endash}H{umlt u}ckel form and the characteristic shielding distance is the dust Debye length. {copyright} {ital 1997 American Institute of Physics.}

Wang, X.; Bhattacharjee, A. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)] [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)

1997-11-01

24

On wave stability in relativistic cosmic-ray hydrodynamics

NASA Technical Reports Server (NTRS)

Wave stability of a two-fluid hydrodynamical model describing the acceleration of cosmic rays by the first-order Fermi mechanism in relativistic, cosmic-ray-modified shocks is investigated. For a uniform background state, the short- and long-wavelength wave speeds are shown to interlace, thus assuring wave stability in this case. A JWKB analysis is performed to investigate the stability of short-wavelength thermal gas sound waves in the smooth, decelerating supersonic flow upstream of a relativistic, cosmic-ray-modified shock. The stability of the waves is assessed both in terms of the fluid velocity and density perturbations, as well as in terms of the wave action. The stability and interaction of the short-wavelength cosmic-ray coherent mode with the background flow is also studied.

Webb, G. M.

1989-01-01

25

Sound damping in ferrofluids: magnetically enhanced compressional viscosity.

The damping of sound waves in magnetized ferrofluids is investigated and shown to be considerably higher than in the nonmagnetized case. This fact may be interpreted as a field-enhanced, effective compressional viscosity-in analogy to the ubiquitous field-enhanced shear viscosity that is known to be the reason for many unusual behaviors of ferrofluids under shear. PMID:12689056

Müller, Hanns Walter; Jiang, Yimin; Liu, Mario

2003-03-01

26

Hydrodynamic shock wave studies within a kinetic Monte Carlo approach

NASA Astrophysics Data System (ADS)

We introduce a massively parallelized test-particle based kinetic Monte Carlo code that is capable of modeling the phase space evolution of an arbitrarily sized system that is free to move in and out of the continuum limit. Our code combines advantages of the DSMC and the Point of Closest Approach techniques for solving the collision integral. With that, it achieves high spatial accuracy in simulations of large particle systems while maintaining computational feasibility. Using particle mean free paths which are small with respect to the characteristic length scale of the simulated system, we reproduce hydrodynamic behavior. To demonstrate that our code can retrieve continuum solutions, we perform a test-suite of classic hydrodynamic shock problems consisting of the Sod, the Noh, and the Sedov tests. We find that the results of our simulations which apply millions of test-particles match the analytic solutions well. In addition, we take advantage of the ability of kinetic codes to describe matter out of the continuum regime when applying large particle mean free paths. With that, we study and compare the evolution of shock waves in the hydrodynamic limit and in a regime which is not reachable by hydrodynamic codes.

Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Howell, Jim; Pickett, Rodney; Staber, Alec; Strother, Terrance

2014-06-01

27

Ferrofluids: Thermophysical properties and formation of microstructures

NASA Astrophysics Data System (ADS)

This work is a combined effort of experimental and theoretical studies toward better understanding the structural and physical properties of aqueous ferrofluids containing nano-sized magnetite (iron oxide magnetic particles) of about 10nm. Ferrofluids have attracted remarkable attention mainly because their properties can be controlled by means of an externally applied magnetic field. The dispersion of nano-sized magnets in a carrier liquid exhibits superparamagnetic behaviour while retaining its fluid properties. The interplay between hydrodynamic and magnetic phenomena has made ferrofluids an extremely promising and useful tool in wide spectra of applications, from technical applications to biomedical ones. In the presence of a magnetic field, magnetic moments of the nanomagnets suspended in the host liquid are aligned toward the field direction and begin to form microstructures such as short chains, strands and long stripes. As this process advances the microstructures may collapse into bundles and thick chains and form macrostructures. Upon the removal of the magnetic field, nanoparticles will be homogeneously redistributed throughout the sample due to thermal agitation. Zero-field structures, and especially the field-induced assembly of magnetic nanoparticles, are primarily responsible for the change in physical properties of ferrofluids, including thermophysical, optical, rheological, and magnetization properties. Because of the field-induced assembly of magnetic nanoparticles in the field direction, ferrofluids become strongly anisotropic and as a result, ferrofluids can significantly enhance directional heat transfer in a thermal system. Thermophysical properties of a ferrofluid are important in studying heat transfer processes in any thermal application, making the study of their behavior a necessity. Taking into account the influence of the formation and growth of microstructures on change in properties of ferrofluids, one can find the significance of identifying and studying the parameters by which ferrofluids' properties can be tailored for a specific need. In Chapter 2 of this dissertation, the influences of magnetic field strength and concentration of ferrofluids on the formation and growth of the chains are observed by employing cryogenic transmission electron microscopy technique. The samples are aqueous magnetite dispersions with concentrations of 0.15%, 0.48% and 0.59% (w/v%). Magnetic field strengths varies from a relatively weak strength of 51.5 mT to the strong field of 0.42 T. Cryo-TEM imaging technique is employed as it allows us to observe the near-native state of the hydrated samples. The cryo-TEM images draw a qualitative comparison basis on the relative significance of magnetic field and concentration on chaining processes. They also provide better understanding of the chains, columns and their internal structures. From a theoretical perspective, an energy equation employing an Eulerian formalism is derived in Chapter 3. Introducing the definition for isotropy and anisotropy of the medium, the equation of heat conduction can be simplified to govern each of the regimes. The equation has taken into account contributions from the important parameters (1) Brownian motion of nanoparticles, (2) magnetic field, (3) temperature, (4) particle size, and (5) volume fraction of particles. In chapter 4, change in effective heat capacity of ferrofluids is addressed and studied with the help of the derivation of the energy equation. The relative significance of the various aforementioned parameters that may have influence on heat capacity of a given medium is quantitatively studied. Lastly, a theoretical model to predict thermal conductivity of a ferrofluid is developed in Chapter 5. From the study on the micrographs, the ferrofluid that becomes anisotropic in the presence of the field is treated as a heterogeneous medium. A structural model, taken into account the anisotropy of the ferrofluid, is introduced in order to develop a theoretical model for effective thermal conductivity of ferrofluids. In order fo

Mousavi Khoeini, NargesSadat Susan

28

Static and dynamic characteristics of magnetized journal bearings lubricated with ferrofluid

This work was concerned with the static and dynamic characteristics of the hydrodynamic journal bearings lubricated with ferrofluid. Based on the momentum and continuity equations, a pressure differential equation (modified Reynolds equation) was obtained. Assuming linear behavior for the magnetic material of the ferrofluid, the magnetic force was calculated. The magnetic pressure resulting from the magnetic force was incorporated into

T. A. Osman; G. S. Nada; Z. S. Safar

2001-01-01

29

National Technical Information Service (NTIS)

The purpose of this study is to investigate the basic magnetization processes and properties of ferrofluids and to apply the findings to the continuum electromechanics in order to develop better models for the magnetically coupled hydrodynamics of these s...

T. B. Jones D. A. Krueger

1974-01-01

30

Ferrofluid and cellulolytic fungi

NASA Astrophysics Data System (ADS)

The study of petroleum ferrofluid influence upon the biology of the cellulolytic fungus Chaetomium globosum, with implications in cellulose biotechnology, was carried out. Taking into account previous results revealing the ferrofluid effects on the cellulose enzyme complex as well as on the dehydrogenases, the results of the investigation of catalase and peroxidase behavior are presented in this paper. The intensification of catalase biosynthesis in response to the increase of hydrogen peroxide after fungus cell interference with the petroleum ferrofluid was the main issue of the experiments.

Manoliu, Al.; Oprica, Lacramioara; Creanga, Dorina-Emilia

2005-03-01

31

Ferrofluids as thermal ratchets.

Colloidal suspensions of ferromagnetic nanoparticles, so-called ferrofluids, are shown to be suitable systems to demonstrate and investigate thermal ratchet behavior: By rectifying thermal fluctuations, angular momentum is transferred to a resting ferrofluid from an oscillating magnetic field without net rotating component. Via viscous coupling the noise driven rotation of the microscopic ferromagnetic grains is transmitted to the carrier liquid to yield a macroscopic torque. For a simple setup we analyze the rotation of the ferrofluid theoretically and show that the results are compatible with the outcome of a simple demonstration experiment. PMID:12935061

Engel, Andreas; Müller, Hanns Walter; Reimann, Peter; Jung, Achim

2003-08-01

32

Transport properties of ferrofluids.

Long-time self-diffusion coefficients of ferrofluid suspensions are derived from an effective Langevin equation approach. The dependences of these transport properties on the volume fraction of particles and the strength of interparticle interaction are investigated. Strong reduction of the rotational and the translational Brownian motion of the particles is manifested upon increase of particle-particle interaction or ferrofluid concentration. PMID:14524753

Hernández-Contreras, M; Ruíz-Estrada, H

2003-09-01

33

Synthesis, physicochemical characterization and MR relaxometry of aqueous ferrofluids.

The synthesis and characterization of ferrofluid based MR contrast agents, which offer R2* versatility beyond that of ferucarbotran, is described. Ferrofluids were formed after stabilizing magnetite cores with dodecanoic acid (a), oleic acid (b), dodecylamine (c), citric acid (d) or tartaric acid (e). Core sizes were deduced from TEM micrographs. Magnetic properties were determined by SQUID magnetometry. Hydrodynamic particle diameters were determined by dynamic light scattering measurements. Zeta potentials were measured by combining laser Doppler velocimetry and phase analysis light scattering. Iron contents were evaluated colorimetrically. MR relaxometry including R1 and R2* was conducted in vitro using homogeneous ferrofluid samples. The average core diameters of ferrofluids a, b and c equaled 9.4 +/- 2.8 nm and approximately 2 nm for ferrofluids d and e. Magnetization measurements at 300 K revealed superparamagnetic behaviour for the dried 9 nm diameter cores and paramagnetic-like behaviour for the dried cores of ferrofluids d and e. Iron contents were between 32-75 mg Fe/mL, reflecting the ferrofluids' high particle concentrations. Hydrodynamic particle diameters equaled 100-120 nm (a, b and c). For the ferrofluids a, b, d and e coated with anions, strong negative zeta potential values between -27.5 mV and -54.0 mV were determined and a positive zeta potential value of +33.5 mV was found for ferrofluid c, covered with cationic dodecylammonium ions. MR relaxometry yielded R1-values of 1.9 +/- 0.3 (a), 4.0 +/- 0.8 (b), 5.2 +/- 1.0 (c), 0.124 +/- 0.002 (d) and 0.092 +/- 0.005 s(-1) mM(-1) (e), and R2*-values of 856 +/- 24 (a), 729 +/- 16 (b), 922 +/- 29 (c), 1.7 +/- 0.05 (d) and 0.49 +/- 0.05 s(-1) mM(-1) (e). Thus, the synthesized ferrofluids reveal a broad spectrum of R2* relaxivities. As a result, the various MR contrast agents have a great potential to be used in studies dealing with malignant tissue targeting or molecular imaging. PMID:18572655

Hodenius, Michael A J; Niendorf, Thoralf; Krombach, Gabriele A; Richtering, Walter; Eckert, Thomas; Lueken, Heiko; Speldrich, Manfred; Günther, Rolf W; Baumann, Martin; Soenen, Stefaan J H; De Cuyper, Marcel; Schmitz-Rode, Thomas

2008-05-01

34

Ferrofluid mediated nanocytometry.

We present a low-cost, flow-through nanocytometer that utilizes a colloidal suspension of non-functionalized magnetic nanoparticles for label-free manipulation and separation of microparticles. Our size-based separation is mediated by angular momentum transfer from magnetically excited ferrofluid particles to microparticles. The nanocytometer is capable of rapidly sorting and focusing two or more species, with up to 99% separation efficiency and a throughput of 3 × 10(4) particles/s per mm(2) of channel cross-section. The device is readily scalable and applicable to live cell sorting with biocompatible ferrofluids, offering competitive cytometer performance in a simple and inexpensive package. PMID:22076536

Kose, Ayse Rezzan; Koser, Hur

2012-01-01

35

This reissue of the classic 1932 edition of Lamb's Hydrodynamics is an indication of the lasting value of the work. Constantly in use since its first publication in 1892, this book is the definitive reference work for all fluid dynamicists. The new foreword by Professor R. Caflisch highlights the prominence of this treatise in the field and outlines the development

Horace Lamb

1993-01-01

36

Generalized Prandtl-Meyer Waves in Relaxation Hydrodynamics.

National Technical Information Service (NTIS)

Three topics are discussed in the paper: (1) the intrinsic forms (expressed in characteristic variables) of the basic equations of relaxation (nonequilibrium) hydrodynamics for three-dimensional, steady flows; (2) the particular form of the above relation...

N. Coburn

1965-01-01

37

Synthesis of ferrofluid with magnetic nanoparticles by sonochemical method for MRI contrast agent

NASA Astrophysics Data System (ADS)

Superparamagnetic iron oxide nanoparticles (SPIO) having high magnetization (83 emu/g) and crystallinity were synthesized by using a sonochemical method. Ferrofluids from these nanoparticles coated with oleic acid as a surfactant were prepared for magnetic resonance imaging (MRI) contrast agent. The coated SPIO could be easily dispersed in chitosan, and the hydrodynamic diameter of the coated SPIO in the chitosan solution was estimated to be 65 nm. The ferrofluids of various concentrations did not agglomerate for 30 days, indicating their good stability. The T1- and T2-weighted MR images of these ferrofluids were obtained and the MRI image contrasts were similar to those of Resovist ®.

Hee Kim, Eun; Sook Lee, Hyo; Kook Kwak, Byung; Kim, Byung-Kee

2005-03-01

38

Structure and Hydrodynamics of Colloidal Systems.

National Technical Information Service (NTIS)

Colloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive o...

J. B. Hayter

1985-01-01

39

We use the modified smoothed particle hydrodynamics (MSPH) method to study the propagation of elastic waves in functionally graded materials. An artificial viscosity is added to the hydrostatic pressure to control oscillations in the shock wave. Computed results agree well with the analytical solution of the problem. It is shown that, for the same placement of particles\\/nodes the MSPH method

G. M. Zhang; R. C. Batra

2007-01-01

40

Full wave solution for hydrodynamic behaviors of pile breakwater

NASA Astrophysics Data System (ADS)

Rayleigh expansion is used to study the water-wave interaction with a row of pile breakwater in finite water depth. Evanescent waves, the wave energy dissipated on the fluid resistance and the thickness of the breakwater are totally included in the model. The formulae of wave reflection and transmission coefficients are obtained. The accuracy of the present model is verified by a comparison with existing results. It is found that the predicted wave reflection and transmission coefficients for the zero order are all highly consistent with the experimental data (Hagiwara, 1984; Isaacson et al., 1998) and plane wave solutions (Zhu, 2011). The losses of the wave energy for the fluid passing through slits play an important role, which removes the phenomena of enhanced wave transmission.

Zhu, Da-tong

2013-06-01

41

NASA Astrophysics Data System (ADS)

In this study, we consider the high dimensional unipolar hydrodynamic model for semiconductors in the form of Euler-Poisson equations. Based on the results that we have obtained in the first part (Huang, et al., 2011 [16]) for the 1-D case, we can further show the stability of planar stationary waves in multi-dimensional case. Utilizing the energy method, we obtain the global existence of the solutions of high dimensional Euler-Poisson equations for the unipolar hydrodynamic model, and prove that the solutions converge to the planar stationary waves time-exponentially.

Huang, Feimin; Mei, Ming; Wang, Yong; Yu, Huimin

42

Particle size analysis in ferrofluids

In this paper we examine the applicability of the Gaussian and lognormal probability functions to describe the distribution of particle sizes found in ferrofluids. Measurements have been made of the particle size distributions contained in a large number of ferrofluids prepared by different techniques. From these measurements we conclude that the form of the distribution may be associated with the

K. O'Grady; A. Bradbury

1983-01-01

43

Hydrodynamic Wave Loading on Offshore Structures Simulated by a Two-Phase Flow Model

The numerical simulation of hydrodynamic wave loading on different types of offshore structures is important to predict forces on and water motion around these structures. This paper presents a numerical study of the effects of two-phase flow on an offshore structure subject to breaking waves.\\u000aThe details of the numerical model, an improved Volume Of Fluid (iVOF) method, are presented

Rik Wemmenhove; Erwin Loots; Arthur E. P. Veldman

2006-01-01

44

Comprehensive Study on the Linear Hydrodynamic Analysis of a Truss Spar in Random Waves

Truss spars are used for oil exploitation in deep and ultra-deep water if storage crude oil is not needed. The linear hydrodynamic analysis of truss spar in random sea wave load is necessary for determining the behaviour of truss spar. This understanding is not only important for design of the mooring lines, but also for optimising the truss spar design.

Roozbeh Mansouri; Hassan Hadidi

2009-01-01

45

Acoustic source model input parameter simulation via hydrodynamic modeling of breaking waves

Low-frequency source models for sound generation from breaking waves based on the collective oscillation of an entrained bubble cloud require a number of input parameters, e.g., void fraction, cloud size, etc. The present effort seeks to obtain simulations of these parameters using a volume of fluid type hydrodynamic model (BUB) to simulate the air entrainment processes occurring within a breaking

Steven L. Means; William G. Szymczak

2003-01-01

46

A Dynamic Analysis of Hydrodynamic Wave Journal Bearings

NASA Technical Reports Server (NTRS)

The purpose of this paper is to study the dynamic behavior of a three-wave journal bearing using a transient approach. The transient analysis permits the determination of the rotor behavior after the fractional frequency whirl appears. The journal trajectory is determined by solving a set of nonlinear equations of motion using the Runge-Katta method. The fluid film forces are computed by integrating the transient Reynolds equation at each time step location of the shaft with respect to the bearing. Because of the large values of the rotational speeds, turbulent effects were included in the computations. The influence of the temperature on the viscosity was also considered. Numerical results were compared to experimenta1 results obtained at the NASA Glenn Research Center. Comparisons of the theoretical results with experimental data were found to be in good agreement. The numerical and experimental results showed that the fluid film of a three-wave journal bearing having a diameter of 30 mm, a length of 27 mm, and a wave amplitude ratio greater than 0.15 is stable even at rotational speeds of 60,000 RPM. For lower wave amplitude ratios, the threshold speed at which the fluid film becomes unstable depends on the wave amplitude and on the supply pocket pressure. Even if the fluid film is unstable, the wave bearing maintains the whirl orbit inside the bearing clearance.

Ene, Nicoleta M.; Dimofte, Florin; Keith, Theo G.

2008-01-01

47

EXPERIMENTAL AND NUMERICAL STUDY OF OSCILLATORY CONVECTION IN FERROFLUIDS

Introduction. Experimental studies of Rayleigh convection in a shallow disk have been conducted for a ferrofluid containing magnetite particles suspended in a kerosene carrier liquid. The oscillatory convection was observed in the entire investigated temperature region. The spiral and other wave regimes were revealed. In zero magnetic fields and in the presence of temperature gradient the flux of magnetic particles

A. Bozhko; G. Putin; P. Bulychev; T. Tynjala; P. Sarkomaa

48

On features of ferrofluid convection caused by barometrical sedimentation

The experimental and numerical studies of Rayleigh convection in a thin cylindrical layer have been conducted for a ferrofluid containing magnetite particles suspended in kerosene carrier liquid. Near the onset of convection, the wave oscillatory convection was observed both in the experiments and in the numerical finite volume simulations. Time periods of temperature oscillations obtained using thermocouples were investigated using

T. Tynjälä; A. Bozhko; P. Bulychev; G. Putin; P. Sarkomaa

2006-01-01

49

Hydrodynamic instabilities in supernova remnants - Self-similar driven waves

NASA Astrophysics Data System (ADS)

An initial study aimed at elucidating the multidimensional aspects of the hydrodynamic instabilities in supernova remnants is presented. Self-similar solutions are found to exist for the interaction of a steep power-law density profile expanding into a relatively flat stationary power-law density profile. Consideration of the pressure and entropy profiles in the shocked 1D flows shows that the flows are subject to convective instability, by a local criterion. The growth rate for the instability becomes very large near the contact discontinuity between the two shocked regions. A linear analysis of the complete self-similar solutions shows that the solutions are unstable above a critical wavenumber and that the growth rate is greatest at the position of the contact discontinuity. The X-ray image of the remnant of SN 1572 (Tycho) shows emission from clumps of supernova ejecta, which is good evidence for instabilities in this remnant.

Chevalier, Roger A.; Blondin, John M.; Emmering, Robert T.

1992-06-01

50

Magnetization of multicomponent ferrofluids.

The solution of the mean spherical approximation (MSA) integral equation for isotropic multicomponent dipolar hard sphere fluids without external fields is used to construct a density functional theory (DFT), which includes external fields, in order to obtain an analytical expression for the external field dependence of the magnetization of ferrofluidic mixtures. This DFT is based on a second-order Taylor series expansion of the free energy density functional of the anisotropic system around the corresponding isotropic MSA reference system. The ensuing results for the magnetic properties are in quantitative agreement with our canonical ensemble Monte Carlo simulation data presented here. PMID:21795777

Szalai, I; Dietrich, S

2011-08-17

51

Calculation of Chemical Detonation Waves With Hydrodynamics and Thermochemical Equation of State

We model detonation waves for solid explosives, using 2-D Arbitrary Lagrange Eulerian (ALE) hydrodynamics, with an equation of state (EOS) based on thermochemical equilibrium, coupled with simple kinetic rate laws for a few reactants. The EOS for the product species is based on either a BKWC EOS or on an exponential-6 potential model, whose parameters are fitted to a wide range of shock Hugoniot and static compression data. We show some results for the non ideal explosive, urea nitrate. Such a model is a powerful tool for studying such processes as initiation, detonation wave propagation and detonation wave propagation as a function of cylindrical radius.

Howard, W M; Fried, L E; Souers, P C; Vitello, P A

2001-08-01

52

Physics in Action: Ferrofluid Fun

NSDL National Science Digital Library

This article describes ferrofluids, which are man-made liquid magnets. The site tells how these liquid magnets are made, what their current uses are, as well as possible future applications. There are also links to research efforts.

Central, Physics

2004-04-08

53

The interaction of a shock wave with a single air hole and a matrix of air holes in PETN, HMX, and TATB has been numerically modeled. The hot-spot formation, interaction, and the resulting buildup toward detonation were computed using three-dimensional numerical Eulerian hydrodynamics with Arrhenius chemical reaction and accurate equations of state according to the hydrodynamic hot-spot model. The basic differences between shock sensitive explosives (PETN, HMX) and shock insensitive explosives (TATB, NQ) may be described using the hydrodynamic hot-spot model. The reactive hydrodynamics of desensitization of heterogeneous explosives by a weak preshock has been numerically modeled. The preshock desensitizes the heterogeneous explosive by closing the air holes and making it more homogeneous. A higher pressure second shock has a lower temperature in the multiple shocked explosive than in single shocked explosives. The multiple shock temperature may be low enough to cause a detonation wave to fail to propagate through the preshocked explosive. 10 refs., 12 figs.

Mader, C.L.; Kershner, J.D.

1985-01-01

54

Magnetic detection of ferrofluid injection zones.

National Technical Information Service (NTIS)

Ferrofluids are stable colloidal suspensions of magnetic particles that can be stabilized in various carrier liquids. In this study the authors investigate the potential of ferrofluids to trace the movement and position of liquids injected in the subsurfa...

S. Borglin G. Moridis A. Becker

1998-01-01

55

Linear and nonlinear dust ion acoustic waves using the two-fluid quantum hydrodynamic model

The linear and nonlinear properties of a dust ion acoustic wave (DIAW) propagating in an electron-dust-ion plasma are investigated from both analytical and numerical perspectives by employing the two-fluid quantum hydrodynamic model. Ions and dust are assumed to be mobile while electrons are considered to be inertialess. Furthermore, quantum effects (diffraction as well as statistic) due to ions and electrons

W. Masood; A. Mushtaq; R. Khan

2007-01-01

56

Numerical simulation of shock wave phenomena in hydrodynamic model of semiconductor devices

We propose a finite element method to investigate the phenomena of shock wave and to simulate the hydrodynamic model in semiconductor devices. An introduction of this model is discussed first. Then some scaling factors and a relationship between the changing variables are discussed. And then, we use a finite element method (P1-iso-P2 element) to discrete the equations. Some boundary conditions

Ning XU; Geng YANG

2007-01-01

57

Synthesis of Aqueous Ferrofluid

NSDL National Science Digital Library

This video lab manual, by the Interdisciplinary Education Group of the University of Wisconsin Ã¢ÂÂ Madison Materials Research Science and Engineering Center (MRSEC), walks students through the process synthesizing aqueous ferrofluids, which "respond to an external magnetic field enabling the solution's location to be controlled through the application of a magnetic field." Each step of the procedure is detailed and accompanied with a video showing it as it is performed. A brief background of the procedure and the necessary safety and laboratory materials are also given. This detailed resource helps students to explore nanotechnology and advanced materials science through hands-on laboratory activities. A printer-friendly version with an example image for each step is also available, perfect for an in-class handout.

Breitzer, Jonathan; Lisensky, George

2009-04-03

58

Ferrofluid field induced flow for microfluidic applications

Exposing a column of ferrofluid to coincident magnetic and thermal fields produces a pressure gradient in the magnetic fluid. As the column of ferrofluid heats up, it loses its attraction to the magnetic field and is displaced by cooler fluid. Subsequently, it is possible to generate a ferrofluid pump with no moving mechanical parts. Until recently, limitations in the magnetic

Lonnie J. Love; John F. Jansen; Tim E. McKnight; Yul Roh; Tommy J. Phelps; Lucas W. Yeary; Glen T. Cunningham

2005-01-01

59

NASA Astrophysics Data System (ADS)

To unravel the relation between hydrodynamic forcing and the dynamics of the tidal flat-salt-marsh ecosystem, we compared hydrodynamic forcing in terms of proxies relevant to bed sediment motion for four tidal flat-salt-marsh ecosystems that were contrasting in terms of wind exposure (sheltered vs. exposed) and lateral development (shrinking vs. expanding). Wave and current field measurements on these four contrasting tidal flat and salt-marsh ecosystems indicated that the hydrodynamic forcing on the bottom sediment (bed shear stress) was strongly influenced by wind-generated waves, more so than by tidal- or wind-drive currents. The measurements further showed that the hydrodynamic forcing decreased considerably landward of the marsh cliff, highlighting a transition from vigorous (tidal flat and pioneer zone) to sluggish (mature marsh) fluid forcing. Spatial wave modeling using measured wind, revealed that the time-integrated wave forcing on the intertidal mudflat in front of the marsh (i.e., the potential bed sediment pickup) was a factor two higher for salt marshes that are laterally shrinking than for laterally expanding marshes, regardless of whether these marshes were exposed to or sheltered from the wind. The same result could not be obtained from a straightforward wind speed and fetch length approach for estimating wave forcing. This confirmed that wave force estimates required spatial modeling to be consistent with the sites trends of shrinking or expanding marshes and wind exposure is not enough to characterize the wave forcing at these sites. Seasonal changes in wave forcing identified from wind measurements potentially provide an alternative mechanism for marsh cliff formation. During the calm summer, fine sediments switches from the water column to the bed. During the following winter, fine sediment is retained within the vegetated regions while being returned to the water column from the bare tidal flats. The continuous slow upward growth of vegetated areas combined with the seasonal cyclic tidal flat elevations, could, during winter, cause a discontinuity at the bare/vegetated boundary. If this discontinuity grows large enough for plant die-off to occur, then a small cliff will form.

Callaghan, D. P.; Bouma, T. J.; Klaassen, P.; van der Wal, D.; Stive, M. J. F.; Herman, P. M. J.

2010-09-01

60

The effect of magnetic fields on flows of ferrofluids enters the basic hydrodynamic equations by an expression for the relaxation of magnetization of the fluid. Despite intense investigations of ferrohydrodynamics, the question of the appropriate approach to describe the magnetization outside equilibrium is still open.By a comparison of experimental and theoretical data of a Taylor–Couette system as a model system,

M. Reindl; A. Leschhorn; M. Lücke; S. Odenbach

2010-01-01

61

This research paper presents an incompressible smoothed particle hydrodynamics (ISPH) technique to investigate a regular wave overtopping on the coastal structure of different types. The SPH method is a mesh-free particle modeling approach that can efficiently treat the large deformation of free surface. The incompressible SPH approach employs a true hydrodynamic formulation to solve the fluid pressure that has less pressure fluctuations. The generation of flow turbulence during the wave breaking and overtopping is modeled by a subparticle scale (SPS) turbulence model. Here the ISPH model is used to investigate the wave overtopping over a coastal structure with and without the porous material. The computations disclosed the features of flow velocity, turbulence, and pressure distributions for different structure types and indicated that the existence of a layer of porous material can effectively reduce the wave impact pressure and overtopping rate. The proposed numerical model is expected to provide a promising practical tool to investigate the complicated wave-structure interactions. PMID:22919291

Pu, Jaan Hui; Shao, SongDong

2012-01-01

62

Application of a Coupled Wave and Hydrodynamic Model over Complex Bathymetry in Eastern Lake Ontario

NASA Astrophysics Data System (ADS)

The Kingston Basin in eastern Lake Ontario is a region with complex bathymetry including islands, shoals and deeper channels. This area can have waves over 5 m in height and storm surges on the order of 1 m, forced by strong westerly fall and winter storm winds. We characterize the waves, hydrodynamics and thermal structure from observations acquired by acoustic Doppler current profilers, thermistor chains, optical backscatter loggers, water level sensors and wave gauges collected over the 2012 winter period. The SWAN and Delft3D coupled models, validated by the observations, are used to simulate the wave and hydrodynamic conditions for two large storm events. The model was forced with forecast data from the Great Lakes Coastal Forecasting System, observations from the National Oceanographic and Atmospheric Administration and Environment Canada. Results indicate that there is strong spatial variability in wave conditions due to refraction and focusing of the bathymetry. Future work will extend the model to determine the potential environmental impacts of offshore wind farm construction in the region.

McCombs, M. P.; Mulligan, R. P.; Boegman, L.; Yerubandi, R. R.

2012-12-01

63

The rogue wave solutions (rational multibreathers) of the nonlinear Schrödinger equation (NLS) are tested in numerical simulations of weakly nonlinear and fully nonlinear hydrodynamic equations. Only the lowest order solutions from 1 to 5 are considered. A higher accuracy of wave propagation in space is reached using the modified NLS equation, also known as the Dysthe equation. This numerical modeling allowed us to directly compare simulations with recent results of laboratory measurements in Chabchoub et al. [Phys. Rev. E 86, 056601 (2012)]. In order to achieve even higher physical accuracy, we employed fully nonlinear simulations of potential Euler equations. These simulations provided us with basic characteristics of long time evolution of rational solutions of the NLS equation in the case of near-breaking conditions. The analytic NLS solutions are found to describe the actual wave dynamics of steep waves reasonably well. PMID:23944540

Slunyaev, A; Pelinovsky, E; Sergeeva, A; Chabchoub, A; Hoffmann, N; Onorato, M; Akhmediev, N

2013-07-01

64

Hydrodynamic instabilities and transverse waves in propagation mechanism of gaseous detonations

NASA Astrophysics Data System (ADS)

The present study examines the role of transverse waves and hydrodynamic instabilities mainly, Richtmyer-Meshkov instability (RMI) and Kelvin-Helmholtz instability (KHI) in detonation structure using two-dimensional high-resolution numerical simulations of Euler equations. To compare the numerical results with those of experiments, Navier-Stokes simulations are also performed by utilizing the effect of diffusion in highly irregular detonations. Results for both moderate and low activation energy mixtures reveal that upon collision of two triple points a pair of forward and backward facing jets is formed. As the jets spread, they undergo Richtmyer-Meshkov instability. The drastic growth of the forward jet found to have profound role in re-acceleration of the detonation wave at the end of a detonation cell cycle. For irregular detonations, the transverse waves found to have substantial role in propagation mechanism of such detonations. In regular detonations, the lead shock ignites all the gases passing through it, hence, the transverse waves and hydrodynamic instabilities do not play crucial role in propagation mechanism of such regular detonations. In comparison with previous numerical simulations present simulation using single-step kinetics shows a distinct keystone-shaped region at the end of the detonation cell.

Mahmoudi, Y.; Mazaheri, K.; Parvar, S.

2013-10-01

65

Tunable optical and magneto-optical properties of ferrofluid in the terahertz regime.

The dielectric property and magneto-optical effects of ferrofluids have been investigated in the terahertz (THz) regime by using THz time-domain spectroscopy. The experiment results show that the refractive index and absorption coefficient of ferrofluid for THz waves rise up with the increase of nanoparticle concentration in the ferrofluid. Moreover, two different THz magneto-optical effects have been found with different external magnetic fields, of which mechanisms have been theoretically explained well by microscopic structure induced refractive index change in the magnetization process and the transverse magneto-optical effect after the saturation magnetization, respectively. This work suggests that ferrofluid is a promising magneto-optical material in the THz regime which has widely potential applications in THz functional devices for THz sensing, modulation, phase retardation, and polarization control. PMID:24663979

Chen, Sai; Fan, Fei; Chang, Shengjiang; Miao, Yinping; Chen, Meng; Li, Jining; Wang, Xianghui; Lin, Lie

2014-03-24

66

Fabrication of Multi-layered Shock Wave Tube for Hydrodynamic Instability Experiment

NASA Astrophysics Data System (ADS)

In inertial confinement fusion (ICF) experiments, the growth of hydrodynamic instability occurred at the layer-to-layer interface of multilayer capsule is of the main importance to obtain ignition and high gain. In order to investigate and simulate the growth of hydrodynamic instability at "SG II"laser facility, we designed and fabricated a multi-layered shock wave tube (MSWT) in this article. The MSWT consisted of four functional units: planar polystyrene (CH) film, Al film with perturbation patterns, polyimide (PI) plastic and cylindrical carbonized-resorcinol-formaldehyde (CRF) aerogel, which were assembled into a cylindrical CH tube. The design, preparation process and assembly process of MSWT were detailed described. The assembly deviations and packaging material were discussed.

Zhu, Xiurong; Zhou, Bin; Xu, Xiang; Zhong, Yanhong; Du, Ai; Li, Yunong; Zhang, Zhihua; Shen, Jun; Wu, Guangming; Ni, Xingyuan

2011-12-01

67

A Stability Analysis for a Hydrodynamic Three-Wave Journal Bearing

NASA Technical Reports Server (NTRS)

The influence of the wave amplitude and oil supply pressure on the dynamic behavior of a hydrodynamic three-wave journal bearing is presented. Both, a transient and a small perturbation technique, were used to predict the threshold to fractional frequency whirl (FFW). In addition, the behavior of the rotor after FFW appeared was determined from the transient analysis. The turbulent effects were also included in the computations. Bearings having a diameter of 30 mm, a length of 27.5 mm, and a clearance of 35 microns were analyzed. Numerical results were compared to experimental results obtained at the NASA GRC. Numerical and experimental results showed that the above-mentioned wave bearing with a wave amplitude ratio of 0.305 operates stably at rotational speeds up to 60,000 rpm, regardless of the oil supply pressure. For smaller wave amplitude ratios, a threshold of stability was found. It was observed that the threshold of stability for lower wave amplitude strongly depends on the oil supply pressure and on the wave amplitude. When the FFW occurs, the journal center maintains its trajectory inside the bearing clearance and therefore the rotor can be run safely without damaging the bearing surfaces.

Ene, Nicoleta M.; Dimofte, Florin; Keith, Theo G., Jr.

2007-01-01

68

NASA Astrophysics Data System (ADS)

From unicellular ciliates to the respiratory epithelium, carpets of cilia display metachronal waves, long-wavelength phase modulations of the beating cycles, which theory suggests may arise from hydrodynamic coupling. Experiments have been limited by a lack of organisms suitable for systematic study of flagella and the flows they create. Using time-resolved particle image velocimetry, we report the discovery of metachronal waves on the surface of the colonial alga Volvox carteri, whose large size and ease of visualization make it an ideal model organism for these studies. An elastohydrodynamic model of weakly coupled compliant oscillators, recast as interacting phase oscillators, reveals that orbit compliance can produce fast, robust synchronization in a manner essentially independent of boundary conditions, and offers an intuitive understanding of a possible mechanism leading to the emergence of metachronal waves.

Brumley, Douglas R.; Polin, Marco; Pedley, Timothy J.; Goldstein, Raymond E.

2012-12-01

69

Magnetoviscosity in dilute ferrofluids from rotational brownian dynamics simulations.

Ferrofluids are suspensions of magnetic nanoparticles which respond to imposed magnetic fields by changing their viscosity without losing their fluidity. Prior work on modeling the behavior of ferrofluids has focused on using phenomenological suspension-scale continuum equations. A disadvantage of this approach is the controversy surrounding the equation describing the rate of change of the ferrofluid magnetization, the so-called magnetization relaxation equation. In this contribution the viscosity of dilute suspensions of spherical magnetic nanoparticles suspended in a Newtonian fluid and under applied shear and constant magnetic fields is studied through rotational brownian dynamics simulations. Simulation results are compared with the predictions of suspension-scale models based on three magnetization relaxation equations. Excellent agreement is observed between simulation results and the predictions of an equation due to Martsenyuk, Raikher, and Shliomis. Good qualitative agreement is observed with predictions of other equations, although these models fail to accurately predict the magnitude and shear rate dependence of the magnetic-field-dependent effective viscosity. Finally, simulation results over a wide range of conditions are collapsed into master curves using a Mason number defined based on the balance of hydrodynamic and magnetic torques. PMID:21230393

Soto-Aquino, D; Rinaldi, C

2010-10-01

70

Smoothed-particle-hydrodynamics modeling of dissipation mechanisms in gravity waves

NASA Astrophysics Data System (ADS)

The smoothed-particle-hydrodynamics (SPH) method has been used to study the evolution of free-surface Newtonian viscous flows specifically focusing on dissipation mechanisms in gravity waves. The numerical results have been compared with an analytical solution of the linearized Navier-Stokes equations for Reynolds numbers in the range 50-5000. We found that a correct choice of the number of neighboring particles is of fundamental importance in order to obtain convergence towards the analytical solution. This number has to increase with higher Reynolds numbers in order to prevent the onset of spurious vorticity inside the bulk of the fluid, leading to an unphysical overdamping of the wave amplitude. This generation of spurious vorticity strongly depends on the specific kernel function used in the SPH model.

Colagrossi, Andrea; Souto-Iglesias, Antonio; Antuono, Matteo; Marrone, Salvatore

2013-02-01

71

Symmetry Breaking Via Global Bifurcations of Modulated Rotating Waves in Hydrodynamics

NASA Astrophysics Data System (ADS)

The combined experimental and numerical study finds a complex mechanism of Z2 symmetry breaking involving global bifurcations for the first time in hydrodynamics. In addition to symmetry breaking via pitchfork bifurcation, the Z2 symmetry of a rotating wave that occurs in Taylor-Couette flow is broken by a global saddle-node-infinite-period (SNIP) bifurcation after it has undergone a Neimark-Sacker bifurcation to a Z2-symmetric modulated rotating wave. Unexpected complexity in the bifurcation structure arises as the curves of cyclic pitchfork, Neimark-Sacker, and SNIP bifurcations are traced towards their apparent merging point. Instead of symmetry breaking due to a SNIP bifurcation, we find a more complex mechanism of Z2 symmetry breaking involving nonsymmetric two-tori undergoing saddle-loop homoclinic bifurcations and complex dynamics in the vicinity of this global bifurcation.

Abshagen, Jan; Lopez, Juan M.; Marques, Francisco; Pfister, Gerd

2005-02-01

72

Smoothed-particle-hydrodynamics modeling of dissipation mechanisms in gravity waves.

The smoothed-particle-hydrodynamics (SPH) method has been used to study the evolution of free-surface Newtonian viscous flows specifically focusing on dissipation mechanisms in gravity waves. The numerical results have been compared with an analytical solution of the linearized Navier-Stokes equations for Reynolds numbers in the range 50-5000. We found that a correct choice of the number of neighboring particles is of fundamental importance in order to obtain convergence towards the analytical solution. This number has to increase with higher Reynolds numbers in order to prevent the onset of spurious vorticity inside the bulk of the fluid, leading to an unphysical overdamping of the wave amplitude. This generation of spurious vorticity strongly depends on the specific kernel function used in the SPH model. PMID:23496634

Colagrossi, Andrea; Souto-Iglesias, Antonio; Antuono, Matteo; Marrone, Salvatore

2013-02-01

73

NASA Astrophysics Data System (ADS)

Autocatalytic reaction fronts between two reacting species in the absence of fluid flow, propagate as solitary waves. The coupling between autocatalytic reaction front and forced simple hydrodynamic flows leads to stationary fronts whose velocity and shape depend on the underlying flow field. We address the issue of the chemico-hydrodynamic coupling between forced advection in porous media and self-sustained chemical waves. Towards that purpose, we perform experiments over a wide range of flow velocities with the well characterized iodate arsenious acid and chlorite-tetrathionate autocatalytic reactions in transparent packed beads porous media. The characteristics of these porous media such as their porosity, tortuosity, and hydrodynamics dispersion are determined. In a pack of beads, the characteristic pore size and the velocity field correlation length are of the order of the bead size. In order to address these two length scales separately, we perform lattice Boltzmann numerical simulations in a stochastic porous medium, which takes into account the log-normal permeability distribution and the spatial correlation of the permeability field. In both experiments and numerical simulations, we observe stationary fronts propagating at a constant velocity with an almost constant front width. Experiments without flow in packed bead porous media with different bead sizes show that the front propagation depends on the tortuous nature of diffusion in the pore space. We observe microscopic effects when the pores are of the size of the chemical front width. We address both supportive co-current and adverse flows with respect to the direction of propagation of the chemical reaction. For supportive flows, experiments and simulations allow observation of two flow regimes. For adverse flow, we observe upstream and downstream front motion as well as static front behaviors over a wide range of flow rates. In order to understand better these observed static state fronts, flow experiments around a single obstacle were used to delineate the range of steady state behavior. A model using the ``eikonal thin front limit'' explains the observed steady states.

Atis, S.; Saha, S.; Auradou, H.; Martin, J.; Rakotomalala, N.; Talon, L.; Salin, D.

2012-09-01

74

Two-temperature hydrodynamics of laser-generated ultrashort shock waves in elasto-plastic solids

NASA Astrophysics Data System (ADS)

Shock-wave generation by ultrashort laser pulses opens new doors for study of hidden processes in materials happened at an atomic-scale spatiotemporal scales. The poorly explored mechanism of shock generation is started from a short-living two-temperature (2T) state of solid in a thin surface layer where laser energy is deposited. Such 2T state represents a highly non-equilibrium warm dense matter having cold ions and hot electrons with temperatures of 1-2 orders of magnitude higher than the melting point. Here for the first time we present results obtained by our new hybrid hydrodynamics code combining detailed description of 2T states with a model of elasticity together with a wide-range equation of state of solid. New hydro-code has higher accuracy in the 2T stage than molecular dynamics method, because it includes electron related phenomena including thermal conduction, electron-ion collisions and energy transfer, and electron pressure. From the other hand the new code significantly improves our previous version of 2T hydrodynamics model, because now it is capable of reproducing the elastic compression waves, which may have an imprint of supersonic melting like as in MD simulations. With help of the new code we have solved a difficult problem of thermal and dynamic coupling of a molten layer with an uniaxially compressed elastic solid. This approach allows us to describe the recent femtosecond laser experiments.

Ilnitsky, Denis K.; Khokhlov, Viktor A.; Inogamov, Nail A.; Zhakhovsky, Vasily V.; Petrov, Yurii V.; Khishchenko, Konstantin V.; Migdal, Kirill P.; Anisimov, Sergey I.

2014-05-01

75

NASA Astrophysics Data System (ADS)

Most rapidly and differentially rotating disk galaxies, in which the sound speed (thermal velocity dispersion) is smaller than the orbital velocity, display graceful spiral patterns. Yet, over almost 240 yr after their discovery in M51 by Charles Messier, we still do not fully understand how they originate. In this first paper of a series, the dynamical behavior of a rotating galactic disk is examined numerically by a high-order Godunov hydrodynamic code. The code is implemented to simulate a two-dimensional flow driven by an internal Jeans gravitational instability in a nonresonant wave-“fluid” interaction in an infinitesimally thin disk composed of stars or gas clouds. A goal of this work is to explore the local and linear regimes of density wave formation, employed by Lin, Shu, Yuan and many others in connection with the problem of spiral pattern of rotationally supported galaxies, by means of computer-generated models and to compare those numerical results with the generalized fluid-dynamical wave theory. The focus is on a statistical analysis of time-evolution of density wave structures seen in the simulations. The leading role of collective processes in the formation of both the circular and spiral density waves (“heavy sound”) is emphasized. The main new result is that the disk evolution in the initial, quasilinear stage of the instability in our global simulations is fairly well described using the local approximation of the generalized wave theory. Certain applications of the simulation to actual gas-rich spiral galaxies are also explored.

Griv, Evgeny; Wang, Hsiang-Hsu

2014-07-01

76

National Technical Information Service (NTIS)

The Sixteenth Symposium on Naval Hydrodynamics was held at the University of California, Berkeley on July 13-18, 1986 under the joint sponsorship of the Office of Naval Research, the University of California at Berkeley, and the National Research Council....

W. C. Webster

1986-01-01

77

Equilibrium structure of ferrofluid aggregates.

We study the equilibrium structure of large but finite aggregates of magnetic dipoles, representing a colloidal suspension of magnetite particles in a ferrofluid. With increasing system size, the structural motif evolves from chains and rings to multi-chain and multi-ring assemblies. Very large systems form single- and multi-wall coils, tubes and scrolls. These structural changes result from a competition between various energy terms, which can be approximated analytically within a continuum model. We also study the effect of external parameters such as magnetic field on the relative stability of these structures. Our results may give insight into experimental data obtained during solidification of ferrofluid aggregates at temperatures where thermal fluctuations become negligible in comparison to inter-particle interactions. These data may also help to experimentally control the aggregation of magnetic particles. PMID:21339625

Yoon, Mina; Tománek, David

2010-11-17

78

Linear and nonlinear dust ion acoustic waves using the two-fluid quantum hydrodynamic model

The linear and nonlinear properties of a dust ion acoustic wave (DIAW) propagating in an electron-dust-ion plasma are investigated from both analytical and numerical perspectives by employing the two-fluid quantum hydrodynamic model. Ions and dust are assumed to be mobile while electrons are considered to be inertialess. Furthermore, quantum effects (diffraction as well as statistic) due to ions and electrons are incorporated. It is emphasized that the linear dispersion characteristics of the DIAW depend on the quantum diffraction effects of both ions and electrons as well as on the dust concentration. The one-dimensional Korteweg-deVries equation is derived for the quantum DIAW using the reductive perturbative technique. It is observed that the quantum electron diffraction term shrinks the width while the dust concentration enhances both the amplitude and width of the soliton.

Masood, W.; Mushtaq, A.; Khan, R. [Theoretical Plasma Physics Division, P. O. Nilore, Islamabad (Pakistan)

2007-12-15

79

The quantum ion-acoustic waves in single-wall carbon nanotubes are studied with the quantum hydrodynamic model, in which the electron and ion components of the nanotubes are regarded as a two-species quantum plasma system. An analytical expression of the dispersion relation is obtained for the linear disturbance. Numerical results show that the frequency of the ion-acoustic wave strongly depends on the

Li Wei; You-Nian Wang

2007-01-01

80

The quantum ion-acoustic waves in single-wall carbon nanotubes are studied with the quantum hydrodynamic model, in which the electron and ion components of the nanotubes are regarded as a two-species quantum plasma system. An analytical expression of the dispersion relation is obtained for the linear disturbance. Numerical results show that the frequency of the ion-acoustic wave strongly depends on the nanotube's radius in the long-wavelength cases.

Wei Li; Wang Younian [Department of Physics and Computer Science, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5 (Canada); Department of Physics, Dalian University of Technology, Dalian 116023 (China)

2007-05-15

81

In this paper we wish to demonstrate to what extent the numerical method regularized smoothed particle hydrodynamics (RSPH) is capable of modelling shocks and shock reflection patterns in a satisfactory manner. The use of SPH based methods to model shock wave problems has been relatively sparse, both due to historical reasons, as the method was originally developed for studies of

M. Omang; S. Børve; J. Trulsen

2006-01-01

82

Study of audio speakers containing ferrofluid

NASA Astrophysics Data System (ADS)

This work validates a method for increasing the radial restoring force on the voice coil in audio speakers containing ferrofluid. In addition, a study is made of factors influencing splash loss of the ferrofluid due to shock. Ferrohydrodynamic analysis is employed throughout to model behavior, and predictions are compared to experimental data.

Rosensweig, R. E.; Hirota, Y.; Tsuda, S.; Raj, K.

2008-05-01

83

Ferrofluid separator for nonferrous scrap separation

NASA Technical Reports Server (NTRS)

Behavior of nonmagnetic objects within separator is essentially function of density, and independent of size or shape of objects. Results show close agreement between density of object and apparent density of ferrofluid required to float it. Results also demonstrate that very high separation rates are achievable by ferrofluid sink-float separation.

Kaiser, R.; Mir, L.

1974-01-01

84

Autocatalytic reaction fronts between two reacting species in the absence of fluid flow, propagate as solitary waves. The coupling between autocatalytic reaction front and forced simple hydrodynamic flows leads to stationary fronts whose velocity and shape depend on the underlying flow field. We address the issue of the chemico-hydrodynamic coupling between forced advection in porous media and self-sustained chemical waves. Towards that purpose, we perform experiments over a wide range of flow velocities with the well characterized iodate arsenious acid and chlorite-tetrathionate autocatalytic reactions in transparent packed beads porous media. The characteristics of these porous media such as their porosity, tortuosity, and hydrodynamics dispersion are determined. In a pack of beads, the characteristic pore size and the velocity field correlation length are of the order of the bead size. In order to address these two length scales separately, we perform lattice Boltzmann numerical simulations in a stochastic porous medium, which takes into account the log-normal permeability distribution and the spatial correlation of the permeability field. In both experiments and numerical simulations, we observe stationary fronts propagating at a constant velocity with an almost constant front width. Experiments without flow in packed bead porous media with different bead sizes show that the front propagation depends on the tortuous nature of diffusion in the pore space. We observe microscopic effects when the pores are of the size of the chemical front width. We address both supportive co-current and adverse flows with respect to the direction of propagation of the chemical reaction. For supportive flows, experiments and simulations allow observation of two flow regimes. For adverse flow, we observe upstream and downstream front motion as well as static front behaviors over a wide range of flow rates. In order to understand better these observed static state fronts, flow experiments around a single obstacle were used to delineate the range of steady state behavior. A model using the "eikonal thin front limit" explains the observed steady states. PMID:23020499

Atis, S; Saha, S; Auradou, H; Martin, J; Rakotomalala, N; Talon, L; Salin, D

2012-09-01

85

Monodispersed aqueous ferrofluids of iron oxide nanoparticle were synthesized by hydrothermal-reduction route. They were characterized by X-ray diffraction analysis, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy and dynamic light scattering. The results showed that certain concentrations of citric acid (CA) are required to obtain only magnetic iron oxides with mean particle sizes around 8 nm. CA acts as a modulator and reducing agent in iron oxide formation which controls nanoparticle size. The XRD, magnetic and heating measurements showed that the temperature and time of hydrothermal reaction can affect the magnetic properties of obtained ferrofluids. The synthesized ferrofluids were stable at pH 7. Their mean hydrodynamic size was around 80 nm with polydispersity index (PDI) of 0.158. The calculated intrinsic loss power (ILP) was 9.4 nHm{sup 2}/kg. So this clean and cheap route is an efficient way to synthesize high ILP aqueous ferrofluids applicable in magnetic hyperthermia. - Graphical abstract: Monodispersed aqueous ferrofluids of iron oxide nanoparticles were synthesized by hydrothermal-reduction method with citric acid as reductant which is an efficient way to synthesize aqueous ferrofluids applicable in magnetic hyperthermia. Highlights: Black-Right-Pointing-Pointer Aqueous iron oxide ferrofluids were synthesized by hydrothermal-reduction route. Black-Right-Pointing-Pointer Citric acid acted as reducing agent and surfactant in the route. Black-Right-Pointing-Pointer This is a facile, low energy and environmental friendly route. Black-Right-Pointing-Pointer The aqueous iron oxide ferrofluids were monodispersed and stable at pH of 7. Black-Right-Pointing-Pointer The calculated intrinsic loss power of the synthesized ferrofluids was very high.

Behdadfar, Behshid, E-mail: bbehdadfar@ma.iut.ac.ir [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Kermanpur, Ahmad [Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Sadeghi-Aliabadi, Hojjat [School of Pharmacy, Isfahan Pharmaceutical Research Center, Isfahan University of Medical Sciences, Isfahan (Iran, Islamic Republic of); Morales, Maria del Puerto [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco 28049, Madrid (Spain); Mozaffari, Morteza [Department of Physics, Razi University, Kermanshah (Iran, Islamic Republic of)

2012-03-15

86

Hydrodynamic bearing lubricated with magnetic fluids

NASA Astrophysics Data System (ADS)

This paper summarizes the work carried out in the development of hydrodynamic lubricated journal bearings with magnetic fluids. Two different fluids have been analyzed, one ferrofluid from FERROTEC APG s10n and one magnetorheological fluid from LORD Corp., MRF122-2ED. Theoretical analysis has been carried out with numerical solutions of Reynolds equation, based on apparent viscosity modulation for ferrofluid and Bingham model for MR fluid. To validate this model, one test bench has been designed, manufactured and set up, where preliminary results shown in this paper demonstrate that magnetic fluids can be used to develop active journal bearings.

Urreta, H.; Leicht, Z.; Sanchez, A.; Agirre, A.; Kuzhir, P.; Magnac, G.

2009-02-01

87

NASA Astrophysics Data System (ADS)

Prediction of ship motions in waves and the role of viscous effects remains an important problem in naval hydrodynamics. A computational fluid dynamics (CFD) solver has been developed which can simulate the unsteady turbulent boundary layer, wave field, and 6DOF dynamics of a floating body in waves. The solver is based upon the Reynolds-averaged Navier-Stokes equations, and volume-of-fluid (VOF) and dynamic-meshing algorithms. It is used to study free-roll, wave-excited roll, and forced heave and sway motions. Solution validation is achieved by comparing roll-amplitude decay, natural frequency, and response amplitude operator (RAO) for a 2D box barge in regular waves to experimental data. As a practical example, a ship hullform, with and without bilge keels, is studied when undergoing prescribed roll, sway, and heave motions. Details of the fluid dynamics and forces and moments will be correlated to motion amplitudes and frequencies.

Smith, Kevin; Paterson, Eric

2008-11-01

88

Controlling ferrofluid permeability across the blood–brain barrier model.

In the present study, an in vitro blood–brain barrier model was developed using murine brain endothelioma cells (b.End3 cells). Confirmation of the blood–brain barrier model was completed by examining the permeability of FITCDextran at increasing exposure times up to 96 h in serum-free medium and comparing such values with values from the literature. After such confirmation, the permeability of five novel ferrofluid (FF) nanoparticle samples, GGB (ferrofluids synthesized using glycine, glutamic acid and BSA), GGC (glycine, glutamic acid and collagen), GGP (glycine, glutamic acid and PVA), BPC (BSA, PEG and collagen) and CPB (collagen, PVA and BSA), was determined using this blood–brain barrier model. All of the five FF samples were characterized by zeta potential to determine their charge as well as TEM and dynamic light scattering for determining their hydrodynamic diameter. Results showed that FF coated with collagen passed more easily through the blood–brain barrier than FF coated with glycine and glutamic acid based on an increase of 4.5% in permeability. Through such experiments, diverse magnetic nanomaterials (such as FF) were identified for: (1) MRI use since they were less permeable to penetrate the blood–brain barrier to avoid neural tissue toxicity (e.g. GGB) or (2) brain drug delivery since they were more permeable to the blood–brain barrier (e.g. CPB). PMID:24457539

Shi, Di; Sun, Linlin; Mi, Gujie; Sheikh, Lubna; Bhattacharya, Soumya; Nayar, Suprabha; Webster, Thomas J

2014-02-21

89

Anisotropic Light Scattering from Ferrofluids

NASA Astrophysics Data System (ADS)

We have investigated the light scattering in DC magnetic fields from aqueous suspensions of Fe3O4 nanoparticles coated with tetra methyl ammonium hydroxide and ?-Fe2O3 nanoparticles embedded in alginate hydrogel. For Fe3O4 ferrofluid, anomalous light scattering behavior was observed when light propagated both parallel and perpendicular to the magnetic fields. This behavior is attributed to the alignment and aggregation of the nanoparticles in chain-like structures. A very different light scattering behavior was observed for ?-Fe2O3 alginate sample where, under the similar conditions, the application of the magnetic field produced no structured change in scattering. We attribute this difference to the absence of chain-like structures and constrained mobility of iron nanoparticles in the alginate sample. The observation is in agreement with our relaxation and dissipative heating results^1 where both samples exhibited Neel relaxation but only the Fe3O4 ferrofluid showed Brownian relaxation. The results suggest that Brownian relaxation and nanoparticle mobility are important for producing non-linear light scattering in such systems. ^1P.P. Vaishnava, R. Tackett, A. Dixit, C. Sudakar, R. Naik, and G. Lawes, J. Appl. Phys. 102, 063914 (2007).

Rablau, Corneliu; Vaishnava, Prem; Naik, Ratna; Lawes, Gavin; Tackett, Ron; Sudakar, C.

2008-03-01

90

Static and Dynamic Magnetic Response in Ferrofluids.

National Technical Information Service (NTIS)

Ferrofluids are technologically important for a variety of applications ranging from biomedicine, hydraulics, to power generation. They are also model systems for the investigation of physics of relaxation phenomena in magnetic nanoparticles. We have done...

H. Ikanth

2007-01-01

91

Optical Negative Refraction in Ferrofluids with Magnetocontrollability.

National Technical Information Service (NTIS)

We numerically demonstrate optical negative refraction in ferrofluids containing isotropic Fe3O4 nanoparticles, each having an isotropic Ag shell, in the presence of an external dc magnetic field H. The all-angle broadband optical negative refraction with...

J. P. Huang K. W. Yu L. Gao Y. Gao Y. M. Liu

2010-01-01

92

Passive Magnetic Bearing with Ferrofluid Stabilization.

National Technical Information Service (NTIS)

A new class of magnetic bearings is shown to exist analytically and is demonstrated experimentally. The class of magnetic bearings utilize a ferrofluid/solid magnet interaction to stabilize the axial degree of freedom of a permanent magnet radial bearing....

R. Jansen E. Dirusso

1996-01-01

93

Ordered macromolecular structures in ferrofluid mixtures

We have observed ordering of dilute dispersions of spherical and cylindrical macromolecules in magnetized ferrofluids. The order results from structural correlations between macromolecular and ferrofluid particles rather than from macroscopic magnetostatic effects. We have aligned elongated macromolecules by this technique and have obtained anisotropic neutron-diffraction patterns, which reflect the internal structure of the macromolecules. The method provides a tool for orienting suspended macromolecular assemblies which are not amenable to conventional alignment techniques.

Hayter, J.B.; Pynn, R.; Charles, S.; Skjeltorp, A.T.; Trewhella, J.; Stubbs, G.; Timmins, P.

1989-04-03

94

Magnetic detection of ferrofluid injection zones

Ferrofluids are stable colloidal suspensions of magnetic particles that can be stabilized in various carrier liquids. In this study the authors investigate the potential of ferrofluids to trace the movement and position of liquids injected in the subsurface using geophysical methods. An ability to track and monitor the movement and position of injected liquids is essential in assessing the effectiveness of the delivery system and the success of the process. Ferrofluids can also provide a significant detection and verification tool in containment technologies, where they can be injected with the barrier liquids to provide a strong signature allowing determination of the barrier geometry, extent, continuity and integrity. Finally, ferrofluids may have unique properties as tracers for detecting preferential flow features (such as fractures) in the subsurface, and thus allow the design of more effective remediation systems. In this report the authors review the results of the investigation of the potential of ferrofluids to trace the movement and position of liquids injected in the subsurface using geophysical methods. They demonstrate the feasibility of using conventional magnetometry for detecting subsurface zones of injected ferrofluids used to trace liquids injected for remediation or barrier formation. The geometrical shapes considered were a sphere, a thin disk, a rectangular horizontal slab, and a cylinder. Simple calculations based on the principles of magnetometry are made to determine the detection depths of FTs. Experiments involving spherical, cylindrical and horizontal slabs show a very good agreement between predictions and measurements.

Borglin, S.; Moridis, G.; Becker, A.

1998-03-01

95

NASA Astrophysics Data System (ADS)

We consider a hydrodynamic-type system of balance equations for mass and momentum closed by the dynamical equation of state taking into account the effects of spatial nonlocality. We study higher symmetry admitted by this system and establish its non-integrability for the generic values of parameters. A system of ODEs obtained from the system under study through the group theory reduction is investigated. The reduced system is shown to possess a family of the homoclinic solutions describing solitary waves of compression and rarefaction. The waves of compression are shown to be unstable. On the contrary, the waves of rarefaction are likely to be stable. Numerical simulations reveal some peculiarities of solitary waves of rarefaction, and, in particular, the recovery of their shape after the collisions.

Vladimirov, Vsevolod A.; Maçzka, Czes?aw; Sergyeyev, Artur; Skurativskyi, Sergiy

2014-06-01

96

Nanoparticle composition of a ferrofluid and its effects on the magnetic properties.

Experiments were carried out on a water-based ferrofluid (gamma-Fe2O3 with carboxydextran shell) using photon correlation spectroscopy (PCS), atomic force microscopy, and magnetic nanoparticle relaxation measurements. The experiments were designed with the aim to relate the Néel signals that are in theory generated by large single core particles with nanoscopic properties, that is, particle size, particle size distribution, shell properties, and aggregation. For this purpose, the ferrofluid was fractionated by magnetic fractionation and size exclusion chromatography. Nanoparticles adsorbed onto positively charged substrates form a two-dimensional monolayer. Their mean core diameters are in the range of 6 to about 20 nm, and particles above 10 nm are mostly aggregates. The hydrodynamic particle diameters are between 13 and 80 nm. The core diameter of the smallest fraction is confirmed by X-ray reflectometry; the surface coverage is controlled by bulk diffusion. Comparison with the hydrodynamic radius yields a shell thickness of 3.8 nm. Considering the shell thickness to be constant for all particles, it was possible to calculate the apparent particle diameter in the original ferrofluid from the PCS signals of all fractions. As expected, the small cores yielded no Néel relaxation signals in freeze-dried samples; however, the fractions containing mostly aggregates yielded Néel relaxation signals. PMID:15835707

Büscher, K; Helm, C A; Gross, C; Glöckl, G; Romanus, E; Weitschies, W

2004-03-16

97

NASA Astrophysics Data System (ADS)

The complex dynamics of the Adriatic Sea are the result of geographical position, orography and bathymetry, as well as rivers discharge and meteorological conditions that influence, more strongly, the shallow northern part. Such complexity requires a constant monitoring of marine conditions in order to support several activities (marine resources management, naval operations, emergency management, shipping, tourism, as well as scientific ones). Platforms, buoys and mooring located in Adriatic Sea supply almost continuously real time punctual information, which can be spatially extended, with some limitations, by drifters and remote sensing. Operational forecasting systems represent valid tools to provide a complete tridimensional coverage of the area, with a high spatial and temporal resolution. The Hydro-Meteo-Clima Service of the Emilia-Romagna Environmental Agency (ARPA-SIMC, Bologna, Italy) and the Dept. of Life and Environmental Sciences of Università Politecnica delle Marche (DISVA-UNIVPM, Ancona, Italy), in collaboration with the Institute of Marine Science of the National Research Council (ISMAR-CNR, Italy) operationally run several wave and hydrodynamic models on the Adriatic Sea. The main implementations are based on the Regional Ocean Modeling System (ROMS), the wave model Simulating WAves Nearshore (SWAN), and the coupling of the former two models in the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) system. Horizontal resolutions of the different systems range from the 2 km of AdriaROMS to the 0.5 km of the recently implemented northern Adriatic COAWST. Forecasts are produced every day for the subsequent 72 hour with hourly resolution. All the systems compute the fluxes exchanged through the interface with the atmosphere from the numerical weather prediction system named COSMO-I7, an implementation for Italy of the Consortium for Small-scale Modeling (COSMO) model, at 7 km horizontal resolution. Considering the several operational implementations currently running, there is the need to: assess their forecast skill; quantitatively evaluate if the new, coupled systems provide better performances than the uncoupled ones; individuate weaknesses and eventual time trends in the forecasts quality, their causes, and actions to improve the systems. This work presents a first effort aimed to satisfy such need. We employ in situ and remote sensing data collected starting from November 2011, in particular: temperature and salinity data collected during several oceanographic cruises, sea surface temperature derived from satellite measurements, waves, sea level and currents measurements from oceanographic buoys and platforms; specific observational activities funded by the Italian Flagship project RITMARE allowed to collect new measurements in NA coastal areas. Data-model comparison is firstly performed with exploratory qualitative comparisons in order to highlight discrepancies between observed and forecasted data, then a quantitative comparison is performed through the computation of standard statistical scores (root mean square error, mean error, mean bias, standard deviation, cross-correlation). Results are plotted in Taylor diagrams for a rapid evaluation of the overall performances.

Busca, Claudia; Coluccelli, Alessandro; Valentini, Andrea; Benetazzo, Alvise; Bonaldo, Davide; Bortoluzzi, Giovanni; Carniel, Sandro; Falcieri, Francesco; Paccagnella, Tiziana; Ravaioli, Mariangela; Riminucci, Francesco; Sclavo, Mauro; Russo, Aniello

2014-05-01

98

Iron(oxide) ferrofluids: synthesis, structure and catalysis

This thesis describes a study on two connecting research subjects concerning ferrofluids, i.e. the synthesis and use of catalytic magnetic colloids and the microstructural behaviour of ferrofluids in general. An interesting application of ferrofluids (dispersions of magnetic colloids) would be their use in catalysis; catalysts attached to the surface of small magnetic particles could in principle be separated magnetically for

Karen Butter

2003-01-01

99

Hydrodynamic roughness is a critical parameter for characterizing bottom drag in boundary layers, and it varies both spatially and temporally due to variation in grain size, bedforms, and saltating sediment. In this paper we investigate temporal variability in hydrodynamic roughness using velocity profiles in the bottom boundary layer measured with a high-resolution acoustic Doppler profiler (PCADP). The data were collected on the ebb-tidal delta off Grays Harbor, Washington, in a mean water depth of 9 m. Significant wave height ranged from 0.5 to 3 m. Bottom roughness has rarely been determined from hydrodynamic measurements under conditions such as these, where energetic waves and medium-to-fine sand produce small bedforms. Friction velocity due to current u*c and apparent bottom roughness z0a were determined from the PCADP burst mean velocity profiles using the law of the wall. Bottom roughness kB was estimated by applying the Grant-Madsen model for wave-current interaction iteratively until the model u*c converged with values determined from the data. The resulting kB values ranged over 3 orders of magnitude (10-1 to 10-4 m) and varied inversely with wave orbital diameter. This range of kB influences predicted bottom shear stress considerably, suggesting that the use of time-varying bottom roughness could significantly improve the accuracy of sediment transport models. Bedform height was estimated from kB and is consistent with both ripple heights predicted by empirical models and bedforms in sonar images collected during the experiment. Copyright 2005 by the American Geophysical Union.

Lacy, J. R.; Sherwood, C. R.; Wilson, D. J.; Chisholm, T. A.; Gelfenbaum, G. R.

2005-01-01

100

We report the experimental observation of multi-bound-soliton solutions of the nonlinear Schrödinger equation (NLS) in the context of hydrodynamic surface gravity waves. Higher-order N-soliton solutions with N=2, 3 are studied in detail and shown to be associated with self-focusing in the wave group dynamics and the generation of a steep localized carrier wave underneath the group envelope. We also show that for larger input soliton numbers, the wave group experiences irreversible spectral broadening, which we refer to as a hydrodynamic supercontinuum by analogy with optics. This process is shown to be associated with the fission of the initial multisoliton into individual fundamental solitons due to higher-order nonlinear perturbations to the NLS. Numerical simulations using an extended NLS model described by the modified nonlinear Schrödinger equation, show excellent agreement with experiment and highlight the universal role that higher-order nonlinear perturbations to the NLS play in supercontinuum generation. PMID:23952405

Chabchoub, A; Hoffmann, N; Onorato, M; Genty, G; Dudley, J M; Akhmediev, N

2013-08-01

101

NASA Astrophysics Data System (ADS)

Millimeter-sized, spherical silicate grains abundant in chondritic meteorites, which are called as chondrules, are considered to be a strong evidence of the melting event of the dust particles in the protoplanetary disk. One of the most plausible scenarios is that the chondrule precursor dust particles are heated and melt in the high-velocity gas flow (shock-wave heating model). We developed the non-linear, time-dependent, and three-dimensional hydrodynamic simulation code for analyzing the dynamics of molten droplets exposed to the gas flow. We confirmed that our simulation results showed a good agreement in a linear regime with the linear solution analytically derived by Sekyia et al. [Sekyia, M., Uesugi, M., Nakamoto, T., 2003. Prog. Theor. Phys. 109, 717-728]. We found that the non-linear terms in the hydrodynamical equations neglected by Sekiya et al. [Sekiya, M., Uesugi, M., Nakamoto, T., 2003. Prog. Theor. Phys. 109, 717-728] can cause the cavitation by producing negative pressure in the droplets. We discussed that the fragmentation through the cavitation is a new mechanism to determine the upper limit of chondrule sizes. We also succeeded to reproduce the fragmentation of droplets when the gas ram pressure is stronger than the effect of the surface tension. Finally, we compared the deformation of droplets in the shock-wave heating with the measured data of chondrules and suggested the importance of other effects to deform droplets, for example, the rotation of droplets. We believe that our new code is a very powerful tool to investigate the hydrodynamics of molten droplets in the framework of the shock-wave heating model and has many potentials to be applied to various problems.

Miura, Hitoshi; Nakamoto, Taishi

2007-05-01

102

Magnetoviscous effect in a maghemite ferrofluid.

An iron oxide ferrofluid with mean particle size of 10.6 nm was synthesized by co-precipitation. The nanoparticles were characterized using X-ray diffraction, transmission electron microscopy, electron energy loss spectroscopy, and dynamic light scattering. The magnetorheological properties of ferrofluid were investigated using a rotating rheometer. The effect of magnetic field on the aggregation of magnetic nanoparticles and rheological behavior were investigated. Moreover the effects of concentration and particle size on the magnetoviscousity of ferrofluid were studied. The results showed that the maghemite is the major magnetic phase. The magnetoviscous effect leads to phase separation at high magnetic fields which is dependent to the concentration. It was shown that the smaller particle sizes which are not contributed in magnetoviscous effect can contribute at higher magnetic fields. PMID:21770177

Ghasemi, E; Mirhabibi, A; Edrissi, M

2011-06-01

103

Adhesion properties of chain-forming ferrofluids.

Denser and highly magnetized ferrofluids exhibit several non-Newtonian behaviors attributed to the formation of magnetic particle chains. We investigate the rheological and adhesive properties during tensile deformation of a confined chain-forming ferrofluid subjected to a radial magnetic field. Both the magnetoviscous contribution to the viscosity and the adhesive force are derived analytically. The response of the system to changes in the length of the chains is examined under zero and nonzero shear circumstances. Our results indicate that the existence of chains has a significant impact on the adhesive strength as well as on the viscosity of the ferrofluid, allowing it to display both shear-thinning and shear-thickening regimes. These findings open up the possibility of monitoring complex rheological responses of such fluids with the assistance of applied magnetic fields, allowing a more accurate assessment of their adhesive properties. PMID:19518329

Lira, Sérgio A; Miranda, José A

2009-04-01

104

Use of ferrofluids in machining of metals

NASA Astrophysics Data System (ADS)

Ferrofluids controlled by an external magnetic field are suitable as lubricants for moving metal machining parts. Empirical relations of the form M sub c = kDt sub bs sup av sup c were established for the unit cutting torque M sub c as function of the drill diameter, the depth of hole t, the feed rate s, and the cutting rate v when holes in Al3V aluminum alloy, TsAM10-5 zinc alloy, VT1 titanium alloy, or 12Cr18Ni10Ti stainless are cut with a drill of R6M5 high-speed steel using a fixture made of nonmagnetic stainless and a ferrofluid based on MVP mineral tool oil as lubricant. Values of the coefficient and the exponents were determined by the Student significance test and Fisher adequacy test. It is found that ferrofluid as lubricant is more effective in machining of nonmagnetic materials.

Podgorkov, V. V.

1985-03-01

105

Correlation of hydrodynamic features with LGA radar backscatter from breaking waves

Backscatter characteristics of 1-4-m-long, mechanically generated breaking waves have been investigated with a C-band frequency modulated continuous wave (FMCW) radar (up to 3.77-cm range resolution) in the large wind-wave tank at the Ocean Engineering Laboratory, University of California, Santa Barbara. The grazing angle was 6°. Wave breaking was caused to occur in the test section due to wave group selfmodulation,

J. Fuchs; D. Regas; T. Waseda; S. Welch; M. P. Tulin

1999-01-01

106

NASA Astrophysics Data System (ADS)

In this paper, we explicate a method of quantum hydrodynamics (QHD) for the study of the quantum evolution of a system of polarized particles. Although we focused primarily on the two-dimensional (2D) physical systems, the method is valid for three-dimensional (3D) and one-dimensional (1D) systems too. The presented method is based upon the Schrödinger equation. Fundamental QHD equations for charged and neutral particles were derived from the many-particle microscopic Schrödinger equation. The fact that particles possess the electric dipole moment (EDM) was taken into account. The explicated QHD approach was used to study dispersion characteristics of various physical systems. We analyzed dispersion of waves in a two-dimensional ion and hole gas placed into an external electric field, which is orthogonal to the gas plane. Elementary excitations in a system of neutral polarized particles were studied for 1D, 2D, and 3D cases. The polarization dynamics in systems of both neutral and charged particles is shown to cause formation of a new type of waves as well as changes in the dispersion characteristics of already known waves. We also analyzed wave dispersion in 2D exciton systems, in 2D electron-ion plasma, and in 2D electron-hole plasma. Generation of waves in 3D-system neutral particles with EDM by means of the beam of electrons and neutral polarized particles is investigated.

Andreev, P. A.; Kuzmenkov, L. S.; Trukhanova, M. I.

2011-12-01

107

Effect of hull geometry on the hydrodynamic response of spar in regular waves

The hydrodynamic response of the floating production systems, especially deep draft spars, is of major concern in the offshore industry for its influence on the selection of suitable drilling and production equipment. A number of response reduction methods are being investigated in view of better motion response and improved design methods. In the present study, experimental and numerical investigations were

S. Nallayarasu; R. Sreeraj; Manusha Murali

2012-01-01

108

In this paper we study the stability of transonic strong shock solutions of the steady-state one-dimensional unipolar hydrodynamic model for semiconductors. The approach is based on the construction of a pseudo-local symmetrizer and on the paradifferential calculus with parameters, which combines the work of Bony–Meyer and the introduction of a large parameter.

Massimiliano D. Rosini

2004-01-01

109

NASA Astrophysics Data System (ADS)

The investigations carried out between 2002 and 2004 during six field experiments within the Operational Radar and Optical Mapping in monitoring hydrodynamic, morphodynamic and environmental parameters for coastal management (OROMA) project aimed to improve the effectiveness of new remote sensing monitoring technologies such as shipborne imaging radars in coastal waters. The coastal monitoring radar of the GKSS Research Center, Geesthacht, Germany, is based on a Kelvin Hughes RSR 1000 X band (9.42 GHz) vertical (VV) polarized river radar and was mounted on board the research vessel Ludwig Prandtl during the experiments in the Lister Tief, a tidal inlet of the German Bight in the North Sea. The important progress realized in this investigation is the availability of calibrated X band radar data. Another central point of the study is to demonstrate the applicability of the quasi-specular scattering theory in combination with the weak hydrodynamic interaction theory for the radar imaging mechanism of the seabed. Radar data have been taken at very low grazing angles ?2.6° of flood and ebb tide-oriented sand wave signatures at the sea surface during ebb tidal current phases. Current speeds perpendicular to the sand wave crest ?0.6 m s-1 have been measured at wind speeds ?4.5 m s-1 and water depths ?25 m. The difference between the maximum measured and simulated normalized radar cross section (NRCS) modulation of the ebb tide-oriented sand wave is 27%. For the flood tide-oriented sand wave, a difference of 21% has been calculated. The difference between the minimum measured and simulated NRCS modulation of the ebb tide-oriented sand wave is 10%, and for the flood tide-oriented sand wave, a value of 43% has been derived. Phases of measured and simulated NRCS modulations correspond to asymmetric sand wave slopes. The results of the simulated NRCS modulation show the qualitative trend but do not always quantitatively match the measured NRCS modulation profiles because the quasi-specular scattering theory at very low grazing angle is a first-order theory.

Hennings, Ingo; Herbers, Dagmar

2006-10-01

110

In this paper, we consider a concentration grating of magnetic nanoparticles optically induced by thermodiffusion in a layer of ferrofluid in the presence of the external homogeneous magnetic field. The applied field is directed along the concentration gradient and leads to the appearance of the internal nonhomogeneous demagnetizing fields. When the system reaches equilibrium, the optical pumping is switched off, and the grating is allowed to relax. We carry out a stability analysis using the Galerkin approach and numerical simulations of the full system of equations to determine the growth rates and the mode amplitudes of the hydrodynamic and concentration perturbations during the relaxation stage. PMID:21929102

Zablotsky, Dmitry; Blums, Elmars

2011-08-01

111

The nonhomogenized dynamic method of cells (NHDMOC) uses a truncated expansion for the particle displacement field; the expansion parameter is the local cell position vector. In the NHDMOC, specifying the cell structure is similar to specifying the spatial grid used in a finite-difference hydrodynamic calculation. The expansion coefficients for the particle displacement field are determined by the equation of motion, any relevant constitutive relations, plus continuity of traction and displacement at all cell boundaries. The authors derive and numerically solve the NHDMOC equations for the first, second, and third-order expansions, appropriate for modeling a plate-impact experiment. The performance of the NHDMOC is tested, at each order, for its ability to resolve a shock-wave front as it propagates through homogeneous and laminated targets. They find for both cases that the displacement field expansion converges rapidly: given the same cell widths, the first-order theory gives only a qualitative description of the propagating stress wave; the second-order theory performs much better; and the third-order theory gives small refinements over the second-order theory. The performance of the third-order NHDMOC is then compared to that of a standard finite-difference hydrodynamic calculation. The two methods differ in that the former uses a finite-difference solution to update the time dependence of the equations, whereas the hydrodynamic calculation uses finite-difference solutions for both the temporal and spatial variables. Both theories are used to model shock-wave propagation in stainless steel arising from high-velocity planar impact. To achieve the same high-quality resolution of the stress and particle velocity profiles, the NHDMOC consistently requires less fine spatial and temporal grids, and substantially less artificial viscosity to control unphysical high-frequency oscillations in the numerical solutions. Finally, the third-order NHDMOC theory is used to calculate the particle velocity for a shock-wave experiment involving an epoxy-graphite laminate. Constitutive relations suitable for the various materials are used. This includes linear and nonlinear elasticity, and when appropriate, viscoelasticity. The results agree well with the corresponding plate-impact experiment, and are compared to the second-order theory of Clements, Johnson, and Hixson.

Clements, B.E.; Johnson, J.N.

1997-09-01

112

The effect of temperature on the anisotropy of ultrasound attenuation in a ferrofluid

NASA Astrophysics Data System (ADS)

This paper reports results of a study on the acoustic properties of a ferrofluid, APG-513A. The anisotropy of the ultrasonic wave absorption coefficient was determined in a sample subjected to an external magnetic field. The measurements were performed in a strong magnetic field HDC = 125 kA m-1, for temperatures of 1-60°C. The dependence of the absorption coefficient of the ultrasonic wave (f = 3.6 MHz) on the angle between the direction of measurement and that of the magnetic field provided important information on the ferrofluid structure in a magnetic field. A comparison of the experimental results with the predictions of the Taketomi theory allowed a determination of the cluster radius and the number density of the colloidal particles. These data allowed us to draw conclusions about the changes in the parameters describing the structure of the ferrofluid at different temperatures. The per cent contribution of the magnetic particles in the cluster structures was estimated. On the basis of the measurements performed, it was possible to establish the proportion of the ultrasonic wave used for excitation of the translational and rotational degrees of freedom. The results revealed a significant effect of temperature on the translational and rotational components of the absorption coefficient. Moreover, the magnetic susceptibility was measured versus the external magnetic field intensity.

Skumiel, A.

2004-11-01

113

Ferrofluid Would Seal Linear-Motion Valve

NASA Technical Reports Server (NTRS)

Proposed valve employs ferrofluid to make tight seal. Seal requires no precisely machined parts, and hand lapping of valve seats are unnecessary. Magnetic fluid fills gap between shaft and annular pole piece in chamber wall. Precise shaft fit is not necessary.

Chandler, J. A.

1983-01-01

114

Passive Magnetic Bearing With Ferrofluid Stabilization

NASA Technical Reports Server (NTRS)

A new class of magnetic bearings is shown to exist analytically and is demonstrated experimentally. The class of magnetic bearings utilize a ferrofluid/solid magnet interaction to stabilize the axial degree of freedom of a permanent magnet radial bearing. Twenty six permanent magnet bearing designs and twenty two ferrofluid stabilizer designs are evaluated. Two types of radial bearing designs are tested to determine their force and stiffness utilizing two methods. The first method is based on the use of frequency measurements to determine stiffness by utilizing an analytical model. The second method consisted of loading the system and measuring displacement in order to measure stiffness. Two ferrofluid stabilizers are tested and force displacement curves are measured. Two experimental test fixtures are designed and constructed in order to conduct the stiffness testing. Polynomial models of the data are generated and used to design the bearing prototype. The prototype was constructed and tested and shown to be stable. Further testing shows the possibility of using this technology for vibration isolation. The project successfully demonstrated the viability of the passive magnetic bearing with ferrofluid stabilization both experimentally and analytically.

Jansen, Ralph; DiRusso, Eliseo

1996-01-01

115

The equations of nearly incompressible fluids. I - Hydrodynamics, turbulence, and waves

NASA Technical Reports Server (NTRS)

An attempt is made to develop a more general theory of nearly incompressible fluids that can then be applied to many different fields. A perturbation expansion is developed for the fully compressible fluid equations which, in the limit of low Mach number (sound or Alfvenic Mach number), reduce to the appropriate incompressible fluid equations. The method developed derives modified systems of fluid equations in which the compressibility effects are admitted only weakly in terms of the incompressible hydrodynamic solutions ('nearly incompressible hydrodynamics'). Molecular viscosity is included self-consistently, and the role of thermal conduction in an ideal fluid is also considered. With heat conduction included, two distinct routes to incompressibility are found to be possible, distinguished according to the relative magnitudes of the temperature, density, and pressure fluctuations.

Zank, G. P.; Matthaeus, W. H.

1991-01-01

116

The efficiency of disintegration of sewage sludge cells microorganisms were characterized using biochemical parameters such as COD, phosphate, ammonium nitrogen and proteins. The investigated process was additionally assessed using the coefficient DD (Degree of Disintegration). It has been demonstrated that a 30-min of hydrodynamic and ultrasonic disintegration causes the soluble COD value increased about 300 mg /L and 190 mg /L (average), while the degree of disintegration reached 24% and 21%, respectively. The efficiency of sewage sludge hydrodynamic and ultrasonic disintegration was confirmed by increased release of phosphate (V) (from 4 to 54 mg PO?(3-) /L and to 50 mg PO?(3-) /L, respectively), ammonium nitrogen (from 1.5 to 4 mg N-NH?(+) /L and to 3.5 mg N-NH?(+) /L, respectively) and proteins (from 5 to 70 mg/L and to 60 mg/L, respectively). The effectiveness of surplus activated sludge disintegration was tested in the infrared spectrum. Changes in absorbance at the specified wavelength attest to a release of i.e., amines, amino acids, amide groups (proteins), phosphates, ammonium salts of carboxylic acid, etc. during disintegration time. Revealing these chemical groups in over-sludge liquids attests to a destructive influence of hydrodynamic and ultrasonic cavitation on activated sludge microorganisms and effective cells lysis. PMID:24117089

Gr?bel, Klaudiusz; Machnicka, Alicja

2014-01-01

117

Heat transfer and flow patterns in ferrofluid convection

NASA Astrophysics Data System (ADS)

Experiments were performed to examine the influence of an external homogeneous magnetic field - transversal or longitudinal - on ferrofluid convection in horizontal, inclined and vertical layers. The integral and local temperature sensors were used for measuring the heat transport across the layer. The flow patterns were visualized by a temperature-sensitive liquid crystal sheet. The results indicate that with the help of a magnetic field it is possible to control the stability and the form of convective motions. A number of non-linear regimes of convection, e.g., spiral-defect chaos, blinking and localized states were observed. The repeated long-wave transients from Rayleigh convection to pure conduction in the case of a horizontal enclosure and to a shear flow under inclination were also revealed. Figs 31, Refs 41.

Bozhko, A. A.; Putin, G. F.

2003-06-01

118

National Technical Information Service (NTIS)

The annex report B1, a sub-project of the B-project (designated: Wave Energy Converters. Generic Technical Evaluation Study) under the DG XII Initiative concerning Preliminary Actions in Wave Energy Research and Development (under the auspices of the Comm...

1993-01-01

119

Microstructure of bidisperse ferrofluids in a thin layer

In this work we present a characterization of the bidisperse ferrofluid microstructures that appear in thin layers of ferrofluid. These layers have been studied by a combination of Langevin dynamics simulations and density functional theory. Our results allow us to compare the microstructures that exist in quasi-two-dimensional ferrofluid nanolayers with the microstructures found in three-dimensional bidisperse ferrofluids. Furthermore, our results allow us to explain the influence of the geometry of the sample on the topology and size-distribution of the observed aggregates of magnetic nanoparticles.

Minina, E. S., E-mail: alla2307@gmail.com; Muratova, A. B. [Ural Federal University, Department of Mathematical Physics (Russian Federation)] [Ural Federal University, Department of Mathematical Physics (Russian Federation); Cerda, J. J. [Campus University de les Illes Balears, Institute for Cross-Disciplinary Physics and Complex Systems (Spain)] [Campus University de les Illes Balears, Institute for Cross-Disciplinary Physics and Complex Systems (Spain); Kantorovich, S. S., E-mail: sue.kantorovich@usu.ru [Ural Federal University, Department of Mathematical Physics (Russian Federation)

2013-03-15

120

Numerical Simulation of Ferrofluid Flow for Subsurface Environmental Engineering Applications

Ferrofluids are suspensions of magnetic particles of diameter approximately 10 nm stabilized by surfactants in carrier liquids. The large magnetic susceptibility of ferrofluids allows the mobilization of ferrofluid through permeable rock and soil by the application of strong external magnetic fields. We have developed simulation capabilities for both miscible and immiscible conceptualizations of ferrofluid flow through porous media in response to magnetic forces arising from the magnetic field of a rectangular permanent magnet. The flow of ferrofluid is caused by the magnetization of the particles and their attraction toward a magnet, regardless of the orientation of the magnet. The steps involved in calculating the flow of ferrofluid are (1) calculation of the external magnetic field, (2) calculation of the gradient of the external magnetic field, (3) calculation of the magnetization of the ferrofluid, and (4) assembly of the magnetic body force term and addition of this term to the standard pressure gradient and gravity force terms. We compare numerical simulations to laboratory measurements of the magnetic field, fluid pressures, and the two-dimensional flow of ferrofluid to demonstrate the applicability of the methods coded in the numerical simulators. We present an example of the use of the simulator for a field-scale application of ferrofluids for barrier verification.

Oldenburg, Curtis M.; Borglin, Sharon E.; Moridis, George J.

1997-05-05

121

Colloids on the frontier of ferrofluids. Rheological properties.

This paper is devoted to the steady-state rheological properties of two new kinds of ferrofluids. One of these was constituted by CoNi nanospheres of 24 nm in diameter, whereas the other by CoNi nanofibers of 56 nm in length and 6.6 nm in width. These ferrofluids were subjected to shear rate ramps under the presence of magnetic fields of different intensity, and the corresponding shear stress values were measured. From the obtained rheograms (shear stress vs shear rate curves) the values of both the static and the dynamic yield stresses were obtained as a function of the magnetic field. The magnetoviscous effect was also obtained as a function of both the shear rate and the magnetic field. The experimental results demonstrate that upon magnetic field application these new ferrofluids develop yield stresses and magnetoviscous effects much greater than those of conventional ferrofluids, based on nanospheres of approximately 10 nm in diameter. Besides some expected differences, such as the stronger magnetorheological effect in the case of ferrofluids based on nanofibers, some intriguing differences are found between the rheological behaviors of nanofiber ferrofluids and nanosphere ferrofluid. First, upon field application the rheograms of nanofiber ferrofluids present N-shaped dependence of the shear stress on the shear rate. The decreasing part of the rheograms takes place at low shear rate. These regions of negative differential viscosity, and therefore, unstable flow is not observed in the case of nanosphere ferrofluids. The second intriguing difference concerns the curvature of the yield stress vs magnetic field curves. This curvature is negative in the case of nanosphere ferrofluid, giving rise to saturation of the yield stress at medium field, as expected. However, in the case of nanofiber ferrofluid this curvature is positive, which means a faster increase of the yield stress with the magnetic field the higher the magnitude of the latter. These interesting differences may be due to the existence of strong interparticle solid friction in the case of nanofiber ferrofluids. Finally, theoretical models for the static yield stress of the ferrofluids were developed. These models consider that upon field application the ferrofluid nanoparticles are condensed in drops of dense phase. These drops tend to be aligned along the field direction, opposing the flow of the ferrofluids and being responsible for the static quasielastic deformation and the yield-stress phenomena. By considering the existence of interparticle dry friction only in the case of nanofiber ferrofluids, the developed models predicted quite well not only the magnitude of the static yield stress but also the differences in curvature of the yield stress vs magnetic field curves. PMID:22432510

López-López, Modesto T; Gómez-Ramírez, Ana; Rodríguez-Arco, Laura; Durán, Juan D G; Iskakova, Larisa; Zubarev, Andrey

2012-04-17

122

Experiments studying the compression and unstable growth of a dense spherical bubble in a gaseous medium subjected to a strong planar shock wave (2.8 < M < 3.4) are performed in a vertical shock tube. The test gas is initially contained in a free-falling spherical soap-film bubble, and the shocked bubble is imaged using planar laser diagnostics. Concurrently, simulations are carried out using a compressible hydrodynamics code in r-z axisymmetric geometry.Experiments and computations indicate the formation of characteristic vortical structures in the post-shock flow, due to Richtmyer-Meshkov and Kelvin-Helmholtz instabilities, and smaller-scale vortices due to secondary effects. Inconsistencies between experimental and computational results are examined, and the usefulness of the current axisymmetric approach is evaluated.

Niederhaus, John [University of Wisconsin-Madison (United States); Ranjan, Devesh [University of Wisconsin-Madison (United States); Anderson, Mark [University of Wisconsin-Madison (United States); Oakley, Jason [University of Wisconsin-Madison (United States); Bonazza, Riccardo [University of Wisconsin-Madison (United States); Greenough, Jeff [Lawrence Livermore National Laboratory (United States)

2005-05-15

123

A landslide block perched on the northern wall of Tidal Inlet, Glacier Bay National Park (Figure 1), has the potential to generate large waves in Tidal Inlet and the western arm of Glacier Bay if it were to fail catastrophically. Landslide-generated waves are a particular concern for cruise ships transiting through Glacier Bay on a daily basis during the summer months. The objective of this study is to estimate the range of wave amplitudes and periods in the western arm of Glacier Bay from a catastrophic landslide in Tidal Inlet. This study draws upon preliminary findings of a field survey by Wieczorek et al. (2003), and evaluates the effects of variations in landslide source parameters on the wave characteristics.

Geist, Eric L.; Jakob, Matthias; Wieczoreck, Gerald F.; Dartnell, Peter

2003-01-01

124

Magnetic flux shock wave and hydrodynamic dendritic instability in type-II superconducting film

NASA Astrophysics Data System (ADS)

Non-equilibrium flux penetration into the Meissner state in type-II superconducting film is studied. Effects of heat dissipation and transport on the motion and stability of the interface between the magnetic flux and flux-free domains are considered. It is shown that the magnetic induction and temperature, form shock wave with a narrow normal front moving with a constant velocity. It is shown that tangential instability is responsible for a crush of the shock wave front. For a sufficiently small heat diffusion constant, a ultrafast dendrite-shaped magnetic flux structure is predicted, while for large thermal diffusion the shock wave front is found to be stable. We conclude that the heat ballistic transport rather than magnetic non-locality in the film plays the essential role in the shock wave front properties. The dendritic velocity increases along with a reciprocal thickness of the film.

Deutsch, E.; Shapiro, B. Ya.; Shapiro, I.

2008-01-01

125

Energy relaxation for transient convection in ferrofluids.

The onset of transient instability driven by a coupling of thermal and magnetic effects in an initially quiescent ferrofluid layer is investigated using the energy method. Following the work of Kim [Phys. Lett. A 372, 4709 (2008)], an energy stability criterion is derived for the underlying dynamical system by taking into account the different boundary conditions and the Prandtl number effects. The critical onset time of the instability is determined as a function of the Rayleigh number, the Prandtl number, and the thermomagnetic parameter. For larger times, our analysis predicts that the energy stability theory and the linear theory yield essentially the same results irrespective of whether the fluid under consideration is a magnetically polarizable or a nonmagnetic fluid and subcritical instabilities are not possible. For the global nonlinear stability boundary in the impulsively heated ferrofluid layer, the minimum critical onset time is found to occur when the values of the Rayleigh number and the thermomagnetic parameter are same. PMID:20866909

Singh, Jitender

2010-08-01

126

Ferrofluid-based microchip pump and valve

Fluid control is a key element in the performance of microfluidic “lab-on-a-chip” devices. The development of integrated multi-function micro-chemical reactors and analysis platforms depends upon on-chip valving and pumping. In this work, microfluidic valves and pumps were fabricated from etched glass substrates each bonded to a second glass substrate lid that had ultrasonically drilled access holes. The devices contained ferrofluid

Herb Hartshorne; Christopher J. Backhouse; William E. Lee

2004-01-01

127

Ferrofluid-based liquid-phase microextraction.

A new mode of liquid-phase microextraction based on a ferrofluid has been developed. The ferrofluid was composed of silica-coated magnetic particles and 1-octanol as the extractant solvent. The 1-octanol was firmly confined within the silica-coated particles, preventing it from being lost during extraction. Sixteen polycyclic aromatic hydrocarbons (PAHs) were used as model compounds in the development and evaluation of the extraction procedure in combination with gas chromatography-mass spectrometry. Parameters affecting the extraction efficiency were investigated in detail. The optimal conditions were as follows: 20mL sample volume, 10mg of the silica-coated magnetic particles (28mg of ferrofluid), agitation at 20Hz, 20min extraction time, and 2min by sonication with 100?L acetonitrile as the final extraction solvent. Under optimal extraction conditions, enrichment factors ranging from 102- to 173-fold were obtained for the analytes. The limits of detection and the limits of quantification were in the range of 16.8 and 56.7pgmL(-1) and 0.06 and 0.19ngmL(-1), respectively. The linearities were between 0.5-100 and 1-100ngmL(-1) for different PAHs. As the ferrofluid can respond to and be attracted by a magnet, the extraction can be easily achieved by reciprocating movement of an external magnet that served to agitate the sample. No other devices were needed in this new approach of extraction. This new technique is affordable, efficient and convenient for microextraction, and offers portability for potential onsite extraction. PMID:20961552

Shi, Zhi-Guo; Zhang, Yufeng; Lee, Hian Kee

2010-11-19

128

Dynamic analysis of hydrodynamic behavior of a flatfish cage system under wave conditions

NASA Astrophysics Data System (ADS)

This paper presents a simulation model based on the finite element method. The method is used to analyze the motion response and mooring line tension of the flatfish cage system in waves. The cage system consists of top frames, netting, mooring lines, bottom frames, and floats. A series of scaled physical model tests in regular waves are conducted to verify the numerical model. The comparison results show that the simulated and the experimental results agree well under the wave conditions, and the maximum pitch of the bottom frame with two orientations is about 12°. The motion process of the whole cage system in the wave can be described with the computer visualized technology. Then, the mooring line tensions and the motion of the bottom frame with three kinds of weight are calculated under different wave conditions. According to the numerical results, the differences in mooring line tensions of flatfish cages with three weight modes are indistinct. The maximum pitch of the bottom frame decreases with the increase of the bottom weight.

Cui, Yong; Guan, Chang-tao; Wan, Rong; Huang, Bin; Li, Jiao

2014-04-01

129

Ferrofluid based micro-electrical energy harvesting

NASA Astrophysics Data System (ADS)

Innovations in energy harvesting have seen a quantum leap in the last decade. With the introduction of low energy devices in the market, micro energy harvesting units are being explored with much vigor. One of the recent areas of micro energy scavenging is the exploitation of existing vibrational energy and the use of various mechanical motions for the same, useful for low power consumption devices. Ferrofluids are liquids containing magnetic materials having nano-scale permanent magnetic dipoles. The present work explores the possibility of the use of this property for generation of electricity. Since the power generation is through a liquid material, it can take any shape as well as response to small acceleration levels. In this work, an electromagnet-based micropower generator is proposed to utilize the sloshing of the ferrofluid within a controlled chamber which moves to different low frequencies. As compared to permanent magnet units researched previously, ferrofluids can be placed in the smallest of containers of different shapes, thereby giving an output in response to the slightest change in motion. Mechanical motion from 1- 20 Hz was able to give an output voltage in mV's. In this paper, the efficiency and feasibility of such a system is demonstrated.

Purohit, Viswas; Mazumder, Baishakhi; Jena, Grishma; Mishra, Madhusha

2013-03-01

130

Condensation and ordering of colloidal spheres dispersed in a ferrofluid

Polystyrene microspheres of the same size dispersed in ferrofluid produce voids which have been denoted magnetic holes. The magnetic moment of one sphere (hole) is equal to the magnetic moment of the ferrofluid displaced by the sphere.The system may essentially be made two-dimensional by confining the dispersion between two glass plates with separation slightly larger than the sphere diameter. It

Arne T. Skjeltorp

1995-01-01

131

Aqueous ferrofluids based on manganese and cobalt ferrites

Synthesis of two new aqueous ferrofluids is performed chemically according to Massart's procedure. Manganese and cobalt ferrite magnetic particles are precipitated and treated in order to obtain colloidal sols by creating a charge density on their surface. Such “ionic” ferrofluids can be prepared in an acidic (after a treatment by ferric nitrate) or in an alkaline medium at a concentration

Francisco Augusto Tourinho; Raymonde Franck; René Massart

1990-01-01

132

Magnetic Field Assisted Fractionation of Nonmagnetic Colloids in Ferrofluid

Flocculation of nonmagnetic colloidal particles in ferrofluid while in the presence of an external uniform magnetic field is investigated experimentally. Magnetic nanoparticles in ferrofluid create magnetic interactions between nonmagnetic colloidal particles. It is demonstrated that nonmagnetic particles can be fractionated by size much more efficiently in the presence of these magnetic interactions

D. Halverson; G. Friedman

2007-01-01

133

It is investigated how hydrodynamic excitations affect the spectrum of various fluctuating quantities and response functions. In solid, the propagating hydrodynamic excitation in phonon gas, that is, second sound contributes to thermal conduction. The corresponding conductivity diverges if the lower limit of the momentum of the excitation decreases to zero. The density fluctuation in the hydrodynamic excitations is polydispersive and

Koichiro Matsuno

1972-01-01

134

Theory of chaos in surface waves: The reduction from hydrodynamics to few-dimensional dynamics

NASA Astrophysics Data System (ADS)

The experiment on chaos in surface waves reported by Ciliberto and Gollub is used as a case model for an understanding of the appearance of few-dimensional chaos in systems with infinite degrees of freedom. Center-manifold and normal-form theories are utilized to derive the pertinent dynamical system and to provide an approximate solution of the partial differential equations. Comparisons of theory and experiment are discussed.

Meron, Ehud; Procaccia, Itamar

1986-03-01

135

For finite adspecies mobility, the lattice-gas monomer-dimer (A+B{sub 2}) surface reaction model exhibits a discontinuous transition from a stable reactive steady state to a stable A-poisoned steady state, as the impingement rate P{sub A} for A increases above a critical value P{sup {asterisk}}. The reactive (poisoned) state is metastable for P{sub A} just above (below) P{sup {asterisk}}. Increasing the surface mobility of A enhances metastability, leading to bistability in the limit of high mobility. In the bistable region, the more stable state displaces the less stable one separated from it by a planar interface, with P{sup {asterisk}} becoming the equistability point for the two states. This hydrodynamic regime can be described by reaction-diffusion equations (RDE{close_quote}s). However, for finite reaction rates, mixed adlayers of A and B are formed, resulting in a coverage-dependent and tensorial nature to chemical diffusion (even in the absence of interactions beyond site blocking). For equal mobility of adsorbed A and B, and finite reaction rate, the prediction for P{sup {asterisk}} from such RDE{close_quote}s, incorporating the appropriate description of chemical diffusion, is shown to coincide with that from kinetic Monte Carlo simulations for the lattice-gas model in the regime of high mobility. Behavior for this special case is compared with that for various other prescriptions of mobility, for both finite and infinite reaction rates. {copyright} {ital 1998} {ital The American Physical Society}

Tammaro, M. [Department of Physics, University of Rhode Island, Kingston, Rhode Island02881 (United States)] [Department of Physics, University of Rhode Island, Kingston, Rhode Island02881 (United States); Evans, J.W. [Ames Laboratory and Department of Mathematics, Iowa State University, Ames, Iowa50011 (United States)] [Ames Laboratory and Department of Mathematics, Iowa State University, Ames, Iowa50011 (United States)

1998-05-01

136

Ion reflection at perpendicular, collisionless shock waves is treated in a simple gas dynamical context. The effect of pickup ions reflected by the cross-shock potential and their subsequent energization in the motional electric field is included through the introduction of source terms in the basic inviscid fluid equations. From a weak source description, a Burgers' equation is derived modified by the addition of a quadratically nonlinear term. The construction of Burgers' equation demonstrates explicitly that particle reflection is a dissipation mechanism for collisionless shocks. Numerical solutions for the modified Burgers' equation (MBE) are presented. From these solutions it is implied that the dissipative term of the MBE is associated with the length scale of the shock foot, while the additional term is associated with the shock ramp. The general physical model is discussed in terms of the reflection and energization of pickup ions at outer heliospheric perpendicular shocks.

Burrows, R. H.; Zank, G. P.; Dasgupta, B.; Webb, G. M. [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville (United States)

2010-12-30

137

Field-Induced Structures in Ferrofluid Emulsions

NASA Astrophysics Data System (ADS)

The field-induced structure in a monodisperse ferrofluid emulsion is studied. An applied magnetic field induces a magnetic dipole moment in each droplet. When the dipole-dipole interaction energy exceeds the thermal energy, a phase transition occurs as the fluid of randomly dispersed droplets changes to a solid of nearly equally sized and spaced columns. Our results show that the column spacing follows a relation d = 1.33L0.37 for cell thickness 3<=L<=800 ?m. A new theory, which treats the column shape more realistically, is developed to account for the results.

Liu, Jing; Lawrence, E. M.; Wu, A.; Ivey, M. L.; Flores, G. A.; Javier, K.; Bibette, J.; Richard, J.

1995-04-01

138

Magnetic and rheological characterization of novel ferrofluids

NASA Astrophysics Data System (ADS)

A new type of magnetic fluid containing silica-coated magnetic nanoparticles has been synthesized. The particles are produced by a flame synthesis and have been dispersed in an oily medium to obtain the magnetic fluid. By means of magnetic and rheological investigations the basic properties of these fluids were determined. It could be seen, that the fluids show the well known paramagnetic behavior of ferrofluids with a small hysteresis due to the large domain size of the magnetic particles. Moreover strong dependencies of the rheological functions on magnetic field strength could be observed.

Kroell, M.; Pridoehl, M.; Zimmermann, G.; Pop, L.; Odenbach, S.; Hartwig, A.

2005-03-01

139

Waves in Radial Gravity Using Magnetic Fluid

NASA Technical Reports Server (NTRS)

We are beginning laboratory experiments using magnetically active ferrofluids to study surface waves in novel geometries. Terrestrial gravity is eliminated from the dynamics, and the magnetic body force felt by ferrofluid in the presence of a magnetic field gradient is used to create a geopotential field which is a section of or an entire sphere or cylinder. New optical, electromagnetic and ultrasonic diagnostic techniques are under development to initially study capillary-gravity wave propagation and interaction in such geometries.

Ohlsen, Daniel R.; Hart, John E.; Weidman, Patrick D.

1996-01-01

140

Elongation of confined ferrofluid droplets under applied fields.

Ferrofluids are strongly paramagnetic liquids. We study the behavior of ferrofluid droplets confined between two parallel plates with a weak applied field parallel to the plates. The droplets elongate under the applied field to reduce their demagnetizing energy and reach an equilibrium shape where the magnetic forces balance against the surface tension. This elongation varies logarithmically with aspect ratio of droplet thickness to its original radius, in contrast to the behavior of unconfined droplets. Experimental studies of a ferrofluid-water-surfactant emulsion confirm this prediction. PMID:11970280

Banerjee, S; Fasnacht, M; Garoff, S; Widom, M

1999-10-01

141

Elongational flow effects on the vortex growth out of Couette flow in ferrofluids

NASA Astrophysics Data System (ADS)

The growth behavior of stationary axisymmetric vortices and of oscillatory, nonaxisymmetric spiral vortices in Taylor-Couette flow of a ferrofluid in between differentially rotating cylinders is analyzed using a numerical linear stability analysis. The investigation is done as a function of the inner and outer cylinder's rotation rates, the axial wave number of the vortex flows, and the magnitude of an applied homogeneous axial magnetic field. In particular, the consequences of incorporating elongational flow effects in the magnetization balance equation on the marginal control parameters that separate growth from decay behavior are determined. That is done for several values of the transport coefficient that measures the strength of these effects.

Altmeyer, S.; Leschhorn, A.; Hoffmann, Ch.; Lücke, M.

2013-05-01

142

Elongational flow effects on the vortex growth out of Couette flow in ferrofluids.

The growth behavior of stationary axisymmetric vortices and of oscillatory, nonaxisymmetric spiral vortices in Taylor-Couette flow of a ferrofluid in between differentially rotating cylinders is analyzed using a numerical linear stability analysis. The investigation is done as a function of the inner and outer cylinder's rotation rates, the axial wave number of the vortex flows, and the magnitude of an applied homogeneous axial magnetic field. In particular, the consequences of incorporating elongational flow effects in the magnetization balance equation on the marginal control parameters that separate growth from decay behavior are determined. That is done for several values of the transport coefficient that measures the strength of these effects. PMID:23767623

Altmeyer, S; Leschhorn, A; Hoffmann, Ch; Lücke, M

2013-05-01

143

Magnetic field effects on viscous fingering of a ferrofluid in an anisotropic Hele-Shaw cell

NASA Astrophysics Data System (ADS)

When a viscous fluid is pushed into a more viscous one in a Hele-Shaw cell, the interface between the two fluids may become unstable, leading to fingering and ramified patterns. Anisotropy can be introduced by engraving a grid in one plate of the cell, allowing one to obtain dendritic patterns. The use of a ferrofluid as one of the viscous fluid is a way to introduce magnetism in the problem, especially the magnetic field as a control parameter. Magnetic field effects on viscous fingering of ferrofluids have already been studied: in a rectangular Hele-Shaw cell, a magnetic field applied in the cell plane is stabilizing when parallel to the interface between the two fluids and destabilizing when normal to the interface. A magnetic field perpendicular to the plane of a radial Hele-Shaw cell has the same destabilizing effect as the pressure. We have studied the effect of a magnetic field, normal to and in the plane of anisotropic radial Hele-Shaw cells te{5}, to characterize the competing effects of hydrodynamics, magnetic field and dipolar energy, and anisotropy. Here we study more precisely the effect of a magnetic field normal to a radial anisotropic Hele-Shaw cell. Figs 8, Refs 9.

Ballou, R.; Molho, P.

2005-12-01

144

Ferrofluid pipe flow in an oscillating magnetic field

NASA Astrophysics Data System (ADS)

Ferrofluid pipe flow in an oscillating magnetic field along the pipe axis is studied theoretically in a wide range of the flow rate. The field-dependent part of viscosity (it can be positive or negative) reveals significant dependence on the flow vorticity, i.e., ferrofluids exhibit non-Newtonian behavior. This is manifested in an alteration of the velocity profile-it ceases to be parabolic-and deviation of the flow rate from the value prescribed by Poiseuille's formula. The presented model based on the conventional ferrohydrodynamic equations and an assumption of the ferrofluid structure fits well experimental data recently obtained by Schumacher, Sellien, Konke, Cader, and Finlayson [``Experiment and simulation of laminar and turbulent ferrofluid pipe flow in an oscillating magnetic field,'' Phys. Rev. E 67, 026308 (2003)].

Krekhov, Alexei P.; Shliomis, Mark I.; Kamiyama, Shinichi

2005-03-01

145

Ferrohydrodynamic evaluation of rotational viscosity and relaxation in certain ferrofluids.

A significant effect of aggregation dynamics for aqueous ferrofluid (AF) and kerosene based ferrofluid (KF) using magnetic field dependent capillary viscosity and magneto-optical relaxation measurements is studied. For better comparison parameters of AF and KF are kept similar. Ferrohydrodynamic equations of chain forming ferrofluids, dilute ferrofluids, and Brownian dynamic simulations are compared. It is observed that the rotational viscosity of AF is larger than that of KF due to field induced aggregates in it and strong dipolar interactions. It is also observed that at ?? ~ 0.04 both AF and KF viscosity becomes almost similar, suggesting similar behavior at that shear rate. The magneto-optical relaxation in AF exhibits nonexponential behavior when relaxed from higher magnetic field and follows irreversible thermodynamics, whereas for KF the relaxation is exponential and follows the effective field method. This discrepancy is explained based on aggregation dynamics of magnetic particles. Results are well described by the corresponding theoretical models. PMID:23005542

Patel, Rajesh

2012-07-01

146

Preparation of magnetic ferrofluids in alternative carrier liquids

NASA Technical Reports Server (NTRS)

Ferrofluids are made by grinding magnetic particles together with a polar surfactant and a nonpolar solvent. The surfactant is adsorbed on the particle surfaces and acts as a coupling agent between the particles and the solvent.

Rosensweig, R. E.

1970-01-01

147

Experimental investigation of magnetically driven flow of ferrofluids in porous media.

National Technical Information Service (NTIS)

This report presents experimental results of the flow of ferrofluids in porous media to investigate the potential for precisely controlling fluid emplacement in porous media using magnetic fields. Ferrofluids are colloidal suspensions of magnetic particle...

S. E. Borglin G. J. Moridis C. M. Oldenburg

1998-01-01

148

National Technical Information Service (NTIS)

Ferrofluids are stable colloidal suspensions of sub-domain sized ferrite particles dispersed in a liquid medium by a suitable surfactant agent. Ferrofluids have been successfully prepared using water, hydrocarbons, esters, diesters, fluorocarbons, and eve...

T. B. Jones D. A. Krueger

1977-01-01

149

Sink-Float Ferrofluid Separator Applicable to Full Scale Nonferrous Scrap Separation.

National Technical Information Service (NTIS)

Design and performance of a ferrofluid levitation separator for recovering nonferrous metals from shredded automobiles are reported. The scrap separator uses an electromagnet to generate a region of constant density within a pool of ferrofluid held betwee...

1973-01-01

150

Method and device for manipulating ferrofluids for use in cementing wells

A device is described for manipulating ferrofluids in a wellbore annulus between a pipe or casing and walls of a well, comprising: (a) means for generating a plurality of alternating magnetic fields distributed in a radial manner, the fields extending into a ferrofluid in the wellbore annulus separating the casing and walls of a subterranean formation; and (b) means for moving and plurality of magnetic fields relative to the ferrofluid, to facilitate movement of the ferrofluid. A method is also discussed for manipulating ferrofluids in a wellbore annulus between a pipe or casing and walls of a well, comprising the steps of: (a) generating at least one magnetic field by a permanently magnetized casing, and magnetic field extending into a ferrofluid in the wellbore annulus separating the casing and walls of a subterranean formation; and (b) moving the casing relative to the ferrofluid, to facilitate movement of the ferrofluid.

Larson, D.B.; Nelson, E.B.

1989-02-07

151

Field induced phase segregation in ferrofluids.

We study the phase segregation in magnetite ferrofluids under the influence of an external magnetic field. A phase with lower nanoparticle density and corresponding higher optical transmission is formed in the bottom of a glass cell in the presence of only a very modest magnetic field gradient (smaller than 25 T/m). The flux density in our magnetic configuration is simulated using finite element methods. Upon switching off the external magnetic field, the low-density phase develops into a 'bubble'-like feature. The kinetics of this 'bubble' in the absence and presence of a magnetic field are described and analyzed in terms of a simple model, which takes into account buoyancy and drag forces. PMID:18774140

Kooij, E S; Gâlc?, A C; Poelsema, B

2008-11-01

152

Magnetic Properties of Dipolar Chains in Ferrofluids

NASA Astrophysics Data System (ADS)

We have investigated the dipole interaction energies per particle and the local dipole field distributions in a frozen-magnetization model of a ferrofluid chain in a saturating magnetic field. A lognormal distribution of particle diameters was assumed. The interaction energies were calculated for one-dimensional arrays of dipoles with moments parallel to the chain. We have computed the energies by various approximations related to the hard sphere particle diameter distribution. A similar approach was followed for the local field distributions. It was found that the energy per particle and mean local field were largely determined by the mean particle diameter, but the distribution of local fields was sensitive to both the mean diameter and the assumptions about spatial correlations between particles of different size. Detailed results are presented for water-soluble Fe3O4/PAA (polyacrylic acid).

Avgin, I.; Huber, D. L.

2014-05-01

153

Lithium ferrite nanoparticles for ferrofluid applications

NASA Astrophysics Data System (ADS)

Nanoparticles of Lithium ferrite in the particle size range of 10 nm have been prepared by a citrate precursor method at a relatively low temperature of 200°C. The particles show characteristic infra red (IR) spectrum of lithium ferrite and broadened X-ray diffraction (XRD) patterns typical of the nanoparticle nature. The sample decomposed at 200°C has the ?-LiFe 5O 8 type (a disordered type of spinel) structure which on annealing at 350°C transforms to the ?-LiFe 5O 8 type (an ordered type spinel) structure as shown by both IR spectra and XRD studies. Magnetization curves indicate a particle size distribution consisting of both ferromagnetic particles and a superparamagnetic fraction. With 4 ?Ms values of 2000 G these particles could be useful for applications in certain low magnetization ferrofluids.

Sankaranarayanan, V. K.; Prakash, Om; Pant, R. P.; Islam, Mohammad

2002-11-01

154

Diamagnetic Particle Separation in Ferrofluid Microflows

NASA Astrophysics Data System (ADS)

Particle separation is important for a wide range of applications. A variety of force fields have been demonstrated to separate particles in microfluidic devices. Magnetic field-induced separation is simple, cheap, and free of fluid heating issues that accompany electric, acoustic, and optical methods. We develop a novel magnetic particle separation method in a curved microchannel with a nearby permanent magnet. This method is capable of separating both magnetic and nonmagnetic particles by size. It is based on the dependence of particle magnetophoresis on the particle size and the particle's distance from the magnet. We present in this talk a continuous separation of 3 ?m- and 5 ?m-diameter polystyrene particles in a ferrofluid flow without magnetic and fluorescent labeling. We also develop a numerical model to simulate the particle separation process.

Xuan, Xiangchun; Liang, Litao

2011-11-01

155

A ferrofluid-based wireless pressure sensor

NASA Astrophysics Data System (ADS)

This paper presents a wireless pressure sensor design based on magnetic fluid displacement over a planar coil and its corresponding inductance change. The design of the pressure sensor is presented followed by its fabrication and characterization. Experimental results show a good correlation with a nonlinear model relating the applied pressure to the change in coil self-resonant frequency. A prototype sensor (radius = 6 mm, thickness = 2 mm) based on the above principal using an oil-based ferrofluid (50 µl, ferrite concentration 2%), a polyimide-embedded planar coil (L = 1 µH), and a 25 µm thick polyimide membrane shows a sensitivity of 3 KHz mmHg-1 with a base-line resonant frequency of f0 = 109 MHz.

Chitnis, Girish; Ziaie, Babak

2013-12-01

156

Magnetic Properties of Dipolar Chains in Ferrofluids

NASA Astrophysics Data System (ADS)

We have investigated the dipole interaction energies per particle and the local dipole field distributions in a frozen-magnetization model of a ferrofluid chain in a saturating magnetic field. A lognormal distribution of particle diameters was assumed. The interaction energies were calculated for one-dimensional arrays of dipoles with moments parallel to the chain. We have computed the energies by various approximations related to the hard sphere particle diameter distribution. A similar approach was followed for the local field distributions. It was found that the energy per particle and mean local field were largely determined by the mean particle diameter, but the distribution of local fields was sensitive to both the mean diameter and the assumptions about spatial correlations between particles of different size. Detailed results are presented for water-soluble Fe3O4/PAA (polyacrylic acid).

Avgin, I.; Huber, D. L.

2014-06-01

157

Linear viscoelasticity of an inverse ferrofluid.

A magnetorheological fluid consisting of colloidal silica spheres suspended in an organic ferrofluid is described. Its linear viscoelastic behavior as a function of frequency, magnetic field strength, and silica volume fraction was investigated with a specially designed magnetorheometer. The storage modulus G' is at least an order of magnitude larger than the loss modulus G" at all magnetic field strengths investigated. G' does depend only weakly on frequency, and linearly on volume fraction. A model is presented for the high frequency limit of the storage modulus G'(infinity). In the model our system is treated as a collection of single noninteracting chains of particles. Assuming a dipolar magnetic interaction, theory and experiment show reasonable agreement at high frequencies. PMID:11970308

de Gans, B J; Blom, C; Philipse, A P; Mellema, J

1999-10-01

158

The evolution of field-induced structure of confined ferrofluid emulsions

The authors report a real-time study of the evolution of the structure of confined ferrofluid emulsions during the ''liquid-solid'' phase transition. A monodisperse oil-in-water ferrofluid emulsion is used. The structure evolution of the emulsion after rapidly applying a magnetic field is probed by the static light scattering. The scattering pattern exhibits pronounced rings reflecting the formation of chains and their coalescence to columns or even ''worm'' structures. The scattering ring is found to decrease in size and brighten in intensity with time. To monitor the structure evolution in time, both the ring peak position in scattering wave vector, q[sub max], and the peak intensity, I[sub max], are measured as a function of time. Both q[sub max] and I[sub max] saturate in less than 0.5 seconds after applying a magnetic field. At a constant cell thickness of 25 [mu]m, the evolution of structure is essentially independent of volume fraction ranging from 0.015 to 0.13. In addition, a very good scaling is found in the scattered light intensity as a function of the scattering wave vector.

Mou, T.; Flores, G.A.; Liu, J. (California State Univ., Long Beach, CA (United States). Dept. of Physics and Astronomy); Bibette, J. (Centre de Recherche Paul Pascal, Pessac (France)); Richard, J. (Rhone-Poulenc Recherches, Aubervilliers (France))

1994-09-01

159

Experimental investigation of magnetically driven flow of ferrofluids in porous media

This report presents experimental results of the flow of ferrofluids in porous media to investigate the potential for precisely controlling fluid emplacement in porous media using magnetic fields. Ferrofluids are colloidal suspensions of magnetic particles stabilized in various carrier liquids. In the presence of an external magnetic field, the ferrofluid becomes magnetized as the particles align with the magnetic field. Potential applications of ferrofluids to subsurface contamination problems include magnetic guidance of reactants to contaminated target zones in the subsurface for in situ treatment or emplacement of containment barriers. Laboratory experiments of magnetically induced ferrofluid flow in porous media in this report demonstrate the potential for mobilizing ferrofluid and controlling fluid emplacement through control of the external magnetic field. The pressures measured in ferrofluid due to the attraction of ferrofluid to a permanent magnet agree well with calculated values. The results show that a predictable pressure gradient is produced in the fluid which is strong near the magnet and drops off quickly with distance. This pressure gradient drives the fluid through sand without significant loss of ferrofluid strength due to filtration or dilution. Flow visualization experiments of ferrofluid in water-filled horizontal Hele-Shaw cells demonstrate that ferrofluid obtains a consistent final arc-shaped configuration around the magnet regardless of initial configuration or flow path toward the magnet. Analogous experiments in actual porous media showed similar features and confirm the ability of ferrofluid to move through porous media by magnetic forces.

Borglin, S.E.; Moridis, G.J.; Oldenburg, C.M.

1998-08-01

160

Effects of an oscillating magnetic field on homogeneous ferrofluid turbulence

NASA Astrophysics Data System (ADS)

This paper presents the results from direct numerical simulations of homogeneous ferrofluid turbulence with a spatially uniform, applied oscillating magnetic field. Due to the strong coupling that exists between the magnetic field and the ferrofluid, we find that the oscillating field can affect the characteristics of the turbulent flow. The magnetic field does work on the turbulent flow and typically leads to an increased rate of energy loss via two dissipation modes specific to ferrofluids. However, under certain conditions this magnetic work results in injection, or a forcing, of turbulent kinetic energy into the flow. For the cases considered here, there is no mean shear and the mean components of velocity, vorticity, and particle spin rate are all zero. Thus, the effects shown are entirely due to the interactions between the turbulent fluctuations of the ferrofluid and the magnetic field. In addition to the effects of the oscillation frequency, we also investigate the effects of the choice of magnetization equation. The calculations focus on the approximate centerline conditions of the relatively low Reynolds number turbulent ferrofluid pipe flow experiments described previously [K. R. Schumacher , Phys. Rev. E 67, 026308 (2003)].

Schumacher, Kristopher R.; Riley, James J.; Finlayson, Bruce A.

2010-01-01

161

Sink-float ferrofluid separator applicable to full scale nonferrous scrap separation

NASA Technical Reports Server (NTRS)

Design and performance of a ferrofluid levitation separator for recovering nonferrous metals from shredded automobiles are reported. The scrap separator uses an electromagnet to generate a region of constant density within a pool of ferrofluid held between the magnetic poles; a saturated kerosene base ferrofluid as able to float all common industrial metals of interest. Conveyors move the scrap into the ferrofluid for separation according to density. Results of scrap mixture separation studies establish the technical feasibility of relatively pure aluminum alloy and zinc alloy fractions from shredded automobile scrap by this ferrofluid levitation process. Economic projections indicate profitable operation for shredders handling more than 300 cars per day.

1973-01-01

162

Structure and hydrodynamics of colloidal systems

Colloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to ..mu..sec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.

Hayter, J.B.

1985-07-01

163

The investigations carried out between 2002 and 2004 during six field experiments within the Operational Radar and Optical Mapping in monitoring hydrodynamic, morphodynamic and environmental parameters for coastal management (OROMA) project aimed to improve the effectiveness of new remote sensing monitoring technologies such as shipborne imaging radars in coastal waters. The coastal monitoring radar of the GKSS Research Center, Geesthacht,

Ingo Hennings; Dagmar Herbers

2006-01-01

164

Structure, synthetic methods, magnetic properties and biomedical applications of ferrofluids.

This paper is aimed at conducting a survey of the synthetic methods and magnetic properties of nanoparticles as ferrofluids used in biomedicine. As compared with other works in the field, the distinctive feature of the current work is the systematic study of recent advances in ferrofluids utilized in hyperthermia and magnetic resonance imaging (MRI). The most important feature for application of ferrofluids is super-paramagnetic behavior of magnetic cores with relatively high saturation magnetization. Although Fe3O4 nanoparticles have traditionally been used in medicine; the modified Mn-ferrite has recently received special attention due to its higher saturation magnetization and r2-relaxivity as a contrast agent in MRI. Co-ferrite nanoparticles are also good candidates for hyperthermia treatment because of their high coercivity and magnetocrystalline anisotropy. The thermal decomposition and hydrothermal methods are good candidates for obtaining appropriate super-paramagnetic particles. PMID:23623058

Shokrollahi, H

2013-07-01

165

Three-dimensional diamagnetic particle deflection in ferrofluid microchannel flows.

Magnetic field-induced particle manipulation is a promising technique for biomicrofluidics applications. It is simple, cheap, and also free of fluid heating issues that accompany other common electric, acoustic, and optical methods. This work presents a fundamental study of diamagnetic particle motion in ferrofluid flows through a rectangular microchannel with a nearby permanent magnet. Due to their negligible magnetization relative to the ferrofluid, diamagnetic particles experience negative magnetophoresis and are repelled away from the magnet. The result is a three-dimensionally focused particle stream flowing near the bottom outer corner of the microchannel that is the farthest to the center of the magnet and hence has the smallest magnetic field. The effects of the particle's relative position to the magnet, particle size, ferrofluid flow rate, and concentration on this three-dimensional diamagnetic particle deflection are systematically studied. The obtained experimental results agree quantitatively with the predictions of a three-dimensional analytical model. PMID:22662037

Liang, Litao; Zhu, Junjie; Xuan, Xiangchun

2011-09-01

166

Experimental demonstration of metamaterial "multiverse" in a ferrofluid.

Extraordinary light rays propagating inside a hyperbolic metamaterial look similar to particle world lines in a 2 + 1 dimensional Minkowski spacetime. Magnetic nanoparticles in a ferrofluid are known to form nanocolumns aligned along the magnetic field, so that a hyperbolic metamaterial may be formed at large enough nanoparticle concentration nH. Here we investigate optical properties of such a metamaterial just below nH. While on average such a metamaterial is elliptical, thermal fluctuations of nanoparticle concentration lead to transient formation of hyperbolic regions (3D Minkowski spacetimes) inside this metamaterial. Thus, thermal fluctuations in a ferrofluid look similar to creation and disappearance of individual Minkowski spacetimes (universes) in the cosmological multiverse. This theoretical picture is supported by experimental measurements of polarization-dependent optical transmission of a cobalt based ferrofluid at 1500 nm. PMID:23787680

Smolyaninov, Igor I; Yost, Bradley; Bates, Evan; Smolyaninova, Vera N

2013-06-17

167

Molecular dynamics study of the primary ferrofluid aggregate formation

NASA Astrophysics Data System (ADS)

Investigations of the phase transitions and self-organization in the magnetic aggregates are of the fundamental and applied interest. The long-range ordering structures described in the Tománek's systematization (M. Yoon, and D. Tománek, 2010 [1]) are not yet obtained in the direct molecular dynamics simulations. The resulted structures usually are the linear chains or circles, or, else, amorphous (liquid) formations. In the present work, it was shown, that the thermodynamically equilibrium primary ferrofluid aggregate has either the long-range ordered or liquid phase. Due to the unknown steric layer force and other model idealizations, the clear experimental verification of the real equilibrium phase is still required. The predicted long-range ordered (crystallized) phase produces the faceting shape of the primary ferrofluid aggregate, which can be recognized experimentally. The medical (antiviral) application of the crystallized aggregates has been suggested. Dynamic formation of all observed ferrofluid nanostructures conforms to the Tománek's systematization.

Tanygin, B. M.; Kovalenko, V. F.; Petrychuk, M. V.; Dzyan, S. A.

2012-11-01

168

Three-dimensional diamagnetic particle deflection in ferrofluid microchannel flows

Magnetic field-induced particle manipulation is a promising technique for biomicrofluidics applications. It is simple, cheap, and also free of fluid heating issues that accompany other common electric, acoustic, and optical methods. This work presents a fundamental study of diamagnetic particle motion in ferrofluid flows through a rectangular microchannel with a nearby permanent magnet. Due to their negligible magnetization relative to the ferrofluid, diamagnetic particles experience negative magnetophoresis and are repelled away from the magnet. The result is a three-dimensionally focused particle stream flowing near the bottom outer corner of the microchannel that is the farthest to the center of the magnet and hence has the smallest magnetic field. The effects of the particle’s relative position to the magnet, particle size, ferrofluid flow rate, and concentration on this three-dimensional diamagnetic particle deflection are systematically studied. The obtained experimental results agree quantitatively with the predictions of a three-dimensional analytical model.

Liang, Litao; Zhu, Junjie; Xuan, Xiangchun

2011-01-01

169

Shape Transformation of Fluctuating Vesicles Filled with a Ferrofluid Emulsion

NASA Astrophysics Data System (ADS)

By transferring inverse double emulsion (O/W/O) droplets from an oil phase into a water phase we have assembled asymmetric vesicles containing monodisperse submicron-sized emulsion droplets, which are made of an oil-based ferrofluid. Under a magnetic field the submicron-sized ferrofluid droplets trapped inside flexible vesicles form chain structures, which depend on the size and the shape of vesicles. The formation of chains of trapped ferrofluid droplets can also induce shape changes in fluctuating vesicles. We examine the metastable shapes of lipid vesicles manipulated by an external magnetic field. The responsive vesicles provide a model system to study the topological and rheological properties of biological membranes. The equilibrium shapes and stability of the vesicles under various ionic strengths are also studied.

Tao, Zhang; Yafei, Wang; Gang, Hu

2005-03-01

170

Magnetic and structural investigations on barium hexaferrite ferrofluids

NASA Astrophysics Data System (ADS)

Barium hexaferrite BaFe 12-2 xTi xCo xO 19 ferrofluids have been prepared using oleic acid as surfactant and Isopar M ® or dodecane as carrier liquid. The ferrite particles were prepared by glass crystallization. Hysteresis parameters, the initial susceptibility versus temperature and the magnetic particle size were obtained by VSM. Ferrofluids with a partly deuterated carrier liquid were investigated by small angle neutron scattering (SANS). SANS curves lead to a bimodal size distribution consisting of single magnetic particles with an organic shell and aggregated particles with an incomplete organic layer.

Müller, R.; Hiergeist, R.; Gawalek, W.; Hoell, A.; Wiedenmann, A.

2002-11-01

171

Ground state microstructure of a ferrofluid thin layer

Using a fine weave of theoretical analysis and computer simulations, we found various aggregates of magnetic single-domain nanoparticles, which can form in a quasi-two-dimensional (q2D) ferrofluid layer at low temperatures. Our theoretical investigation allowed us to obtain exact expressions and their asymptotes for the energies of each configuration. Thus, for ferrofluid q2D layers it proved possible to identify the ground states as a function of the particle number, size, and other system parameters. Our suggested approach can be used for the investigation of ground state structures in systems with more complex interparticle interactions.

Prokopieva, T. A.; Danilov, V. A.; Kantorovich, S. S., E-mail: sofia@icp.uni-stuttgart.de [Ural State University (Russian Federation)

2011-09-15

172

Structure and thermodynamics of a ferrofluid monolayer

We model a disordered planar monolayer of paramagnetic spherical particles, or ferrofluid, as a two-dimensional fluid of hard spheres with embedded three-dimensional magnetic point dipoles. This model, in which the orientational degrees of freedom are three dimensional while particle positions are confined to a plane, can be taken as a crude representation of a colloidal suspension of superparamagnetic particles confined in a water/air interface, a system that has recently been studied experimentally. In this paper, we propose an Ornstein-Zernike integral equation approach capable of describing the structure of this highly inhomogeneous fluid, including the effects of an external magnetic field. The method hinges on the use of specially tailored orthogonal polynomials whose weight function is precisely the one-particle distribution function that describes the surface- and field-induced anisotropy. The results obtained for various particle densities and external fields are compared with Monte Carlo simulations, illustrating the capability of the inhomogeneous Ornstein-Zernike equation and the proposed solution scheme to yield a detailed and accurate description of the spatial and orientational structure for this class of systems. For comparison, results from density-functional theory in the modified mean-field approximation are also presented; this latter approach turns out to yield at least qualitatively correct results. PMID:11088163

Lomba; Lado; Weis

2000-04-01

173

Heat transfer and flow patterns in ferrofluid convection

Experiments were performed to examine the influence of an external homogeneous magnetic field - transversal or longitudinal - on ferrofluid convection in horizontal, inclined and vertical layers. The integral and local temperature sensors were used for measuring the heat transport across the layer. The flow patterns were visualized by a temperature-sensitive liquid crystal sheet. The results indicate that with the

A. A. Bozhko; G. F. Putin

2003-01-01

174

Alginate-based ferrofluid and magnetic microsphere thereof.

The Fe(3)O(4) ferrofluids have been prepared using sodium alginate (Na-AL) as a stabilizing agent. The alginate can prevent the aggregation of magnetic nanoparticles and hence contributed to higher stability for the ferrofluids. Furthermore, the alginate component in the ferrofluids was crosslinked by Ca(2+) to produce magnetic microspheres. The swelling behavior of magnetic microspheres showed a pH-dependence, and hence determined the drug release process under various pH conditions. The presence of the Fe(3)O(4) nanoparticles made the magnetic microspheres swell more easily. Meanwhile, the strong ability to absorb the drug for the incorporated Fe(3)O(4) nanoparticles decreased the release rate and hence was more favorable to the sustaining release of drug. Except for the controlled delivery and release of drug, the alginate-based ferrofluids and magnetic microspheres in this work might also show a great potential for other biomedical and biotechnological applications, such as, magnetic targeting, magnetic separation and magnetic resonance imaging. PMID:20797404

Xu, Peihu; Guo, Fengfeng; Huang, Jin; Zhou, Shaofeng; Wang, Daxin; Yu, Jiahui; Chen, Jinghua

2010-12-01

175

Magnetophoresis of ferrofluid in microchannel system and its nonlinear effect

We have studied the magnetophoretic particle separation and its nonlinear behavior of ferrofluids in microchannel which is proposed by Furlani. The magnetic gradient force is caused by an bias field and the polarized magnets and is found to be spatially uniform in the channel section which can be used for particle selecting or separation. We have derived the equations of

Y. C. Jian; L. F. Zhang; J. P. Huang

2006-01-01

176

Magnetic Sensing with Ferrofluid and Fiber Optic Connectors

A simple, cost effective and sensitive fiber optic magnetic sensor fabricated with ferrofluid and commercially available fiber optic components is described in this paper. The system uses a ferrofluid infiltrated extrinsic Fabry-Perot interferometer (EFPI) interrogated with an infrared wavelength spectrometer to measure magnetic flux density. The entire sensing system was developed with commercially available components so it can be easily and economically reproduced in large quantities. The device was tested with two different ferrofluid types over a range of magnetic flux densities to verify performance. The sensors readily detected magnetic flux densities in the range of 0.5 mT to 12.0 mT with measurement sensitivities in the range of 0.3 to 2.3 nm/mT depending on ferrofluid type. Assuming a conservative wavelength resolution of 0.1 nm for state of the art EFPI detection abilities, the estimated achievable measurement resolution is on the order 0.04 mT. The inherent small size and basic structure complimented with the fabrication ease make it well-suited for a wide array of research, industrial, educational and military applications.

Homa, Daniel; Pickrell, Gary

2014-01-01

177

Magnetic sensing with ferrofluid and fiber optic connectors.

A simple, cost effective and sensitive fiber optic magnetic sensor fabricated with ferrofluid and commercially available fiber optic components is described in this paper. The system uses a ferrofluid infiltrated extrinsic Fabry-Perot interferometer (EFPI) interrogated with an infrared wavelength spectrometer to measure magnetic flux density. The entire sensing system was developed with commercially available components so it can be easily and economically reproduced in large quantities. The device was tested with two different ferrofluid types over a range of magnetic flux densities to verify performance. The sensors readily detected magnetic flux densities in the range of 0.5 mT to 12.0 mT with measurement sensitivities in the range of 0.3 to 2.3 nm/mT depending on ferrofluid type. Assuming a conservative wavelength resolution of 0.1 nm for state of the art EFPI detection abilities, the estimated achievable measurement resolution is on the order 0.04 mT. The inherent small size and basic structure complimented with the fabrication ease make it well-suited for a wide array of research, industrial, educational and military applications. PMID:24573312

Homa, Daniel; Pickrell, Gary

2014-01-01

178

Thermodynamics of ferrofluids in applied magnetic fields

NASA Astrophysics Data System (ADS)

The thermodynamic properties of ferrofluids in applied magnetic fields are examined using theory and computer simulation. The dipolar hard sphere model is used. The second and third virial coefficients (B2 and B3) are evaluated as functions of the dipolar coupling constant ?, and the Langevin parameter ?. The formula for B3 for a system in an applied field is different from that in the zero-field case, and a derivation is presented. The formulas are compared to results from Mayer-sampling calculations, and the trends with increasing ? and ? are examined. Very good agreement between theory and computation is demonstrated for the realistic values ??2. The analytical formulas for the virial coefficients are incorporated in to various forms of virial expansion, designed to minimize the effects of truncation. The theoretical results for the equation of state are compared against results from Monte Carlo simulations. In all cases, the so-called logarithmic free energy theory is seen to be superior. In this theory, the virial expansion of the Helmholtz free energy is re-summed in to a logarithmic function. Its success is due to the approximate representation of high-order terms in the virial expansion, while retaining the exact low-concentration behavior. The theory also yields the magnetization, and a comparison with simulation results and a competing modified mean-field theory shows excellent agreement. Finally, the putative field-dependent critical parameters for the condensation transition are obtained and compared against existing simulation results for the Stockmayer fluid. Dipolar hard spheres do not undergo the transition, but the presence of isotropic attractions, as in the Stockmayer fluid, gives rise to condensation even in zero field. A comparison of the relative changes in critical parameters with increasing field strength shows excellent agreement between theory and simulation, showing that the theoretical treatment of the dipolar interactions is robust.

Elfimova, Ekaterina A.; Ivanov, Alexey O.; Camp, Philip J.

2013-10-01

179

Many structural components contain, or are submerged in, a fluid. The fluid moving with a vibrating structure has an important effect on the dynamics of the structure, particularly on its natural frequencies. The effect of the fluid on natural frequencies can be accounted for using the hydrodynamic mass associated with the structure. This paper provides formulas, graphs, and computer programs for calculating hydrodynamic mass.

Chung, H.; Chen, S.S.

1984-01-01

180

Synchronization via Hydrodynamic Interactions

NASA Astrophysics Data System (ADS)

An object moving in a viscous fluid creates a flow field that influences the motion of neighboring objects. We review examples from nature in the microscopic world where such hydrodynamic interactions synchronize beating or rotating filaments. Bacteria propel themselves using a bundle of rotating helical filaments called flagella which have to be synchronized in phase. Other micro-organisms are covered with a carpet of smaller filaments called cilia on their surfaces. They beat highly synchronized so that metachronal waves propagate along the cell surfaces. We explore both examples with the help of simple model systems and identify generic properties for observing synchronization by hydrodynamic interactions.

Kendelbacher, Franziska; Stark, Holger

2013-12-01

181

A method for calculating the energy take-out from a single wave energy converter is presented. The converter consists of a buoy connected via a hose pump to a submerged plate. The equations of motion of the buoy and plate are solved linearly in the frequency domain, which shows that frequency dependent hydrodynamic properties can be used. The emphasis in the

L. Berggren

1992-01-01

182

Dynamics of Single Chains of Suspended Ferrofluid Particles

NASA Technical Reports Server (NTRS)

We present an experimental study of the dynamics of isolated chains made of super-paramagnetic particles under the influence of a magnetic field. The motivation of this work is to understand if the chain fluctuations exist and, if it does, how does the fluctuation affect chain aggregation. We find that single chains strongly fluctuate and that the characteristic frequency of their fluctuations is inversely proportional to the magnetic field strength. The higher the field the lower the characteristic frequency of the chain fluctuations. In the high magnetic field limit, chains behave like rigid rods without any internal motions. In this work, we used ferrofluid particles suspended in water. These particles do not have any intrinsic magnetization. Once a magnetic field is applied, a dipole moment is induced in each particle, proportional to the magnetic field. A dipolar magnetic interaction then occurs between particles. If dipole-dipole magnetic energy is higher than the thermal energy, the result is a structure change inside the dipolar fluid. The ratio of these two energies is expressed by a coupling constant lambda as: lambda = (pi(a(exp 3))(chi(exp 2))(mu(sub 0))(H(sub 0))(exp 2))/18kT Where a is the particle radius, mu(sub 0) is the vacuum magnetic permeability, H(sub 0) the applied magnetic field, k the Boltzmann constant and T the absolute temperature. If lambda > 1, magnetic particles form chains along the field direction. The lateral coalescence of several chains may form bigger aggregates especially if the particle volume fraction is high. While many studies and applications deal with the rheological properties and the structural changes of these dipolar fluids, this work focuses on the understanding of the chain dynamics. In order to probe the chain dynamics, we used dynamic light scattering (DLS) in self-beating mode as our experimental technique. The experimental geometry is such that the scattering plane is perpendicular to the magnetic field. Therefore, only motions in this plane are probed. A very dilute sample of a ferrofluid emulsion with a particle volume fraction of 10(exp -5) is used in this experiment. We chose such a low volume fraction to avoid multiple light scattering as well as lateral chain-chain aggregation. DLS measures the dynamic structure factor S(q,t) of the sample (q is the scattering wave vector, t is the time). In the absence of the magnetic field, identical particles of ferrofluid droplets are randomly distributed and S(q,t) reduces to exp(-q(exp 2)2D(sub 0)t). D(sub 0)=(kT/(6(pi)(eta)(a)) is the diffusion coefficient of Brownian particles (where Xi = (6(pi)(eta)(a)) is the Stokes frictional coefficient of a spherical particle in a fluid of viscosity eta). If interactions or polydispersity can not be ignored, an effective diffusion coefficient is introduced. Formally, D(sub eff) is defined as: D(sub eff) = - q(exp -2) partial derivative of (ln(S(q,t)) with respect to time, as t goes to 0. D(sub eff) reduces to D(sub 0) if no interactions and only a few particles size are present. Therefore, we can use DLS to measure particle size. The particle radius was found to be a=0.23 mu m with 7% of polydispersity. In this case, if we vary the scattering angle theta (and so q) we do not have any change in the measured diffusion coefficient: it is q-independent. When a magnetic field is applied, particles aggregate into chains if lambda > 1. We first studied the kinetics of the chain formation when lambda = 406. At a fixed scattering angle, we measured diffusion coefficient D(sub eff) as a function of time. Experimentally, we find that D(sub eff) decreases monotonously with time. Physically, this means that chains are becoming longer and longer. Since we are only sensitive to motions in the scattering plane and since chains have their main axis perpendicular to this plane, the measured diffusion coefficient is the trans-verse diffusion coefficient. We can relate D(sub eff) to the mean number of particles per chain N(t) at a given time and to the diffusion coefficient of an isolated particle

Cutillas, S.; Liu, J.

1999-01-01

183

Aspects of causal viscous hydrodynamics

We investigate the phenomenology of freely expanding fluids, with different material properties, evolving through the Israel-Stewart (IS) causal viscous hydrodynamics, and compare our results with those obtained in the relativistic Eckart-Landau-Navier-Stokes (ELNS) acausal viscous hydrodynamics. Through the analysis of scaling invariants we give a definition of thermalization time that can be self-consistently determined in viscous hydrodynamics. Next we construct the solutions for one-dimensional boost-invariant flows. Expansion of viscous fluids is slower than that of one-dimensional ideal fluids, resulting in entropy production. At late times, these flows are reasonably well approximated by solutions obtained in ELNS hydrodynamics. Estimates of initial energy densities from observed final values are strongly dependent on the dynamics one chooses. For the same material, and the same final state, IS hydrodynamics gives the smallest initial energy density. We also study fluctuations about these one-dimensional boost-invariant backgrounds; they are damped in ELNS hydrodynamics but can become sound waves in IS hydrodynamics. The difference is obvious in power spectra due to clear signals of wave-interference in IS hydrodynamics, which is completely absent in ELNS dynamics.

Bhalerao, R. S.; Gupta, Sourendu [Department of Theoretical Physics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India)

2008-01-15

184

We present a low-cost, reconfigurable, parallel optofluidic switch that exploits the optical and magnetic properties of water-based ferrofluid. Each switch is composed of an integrated waveguide orthogonally crossing a microfluidic channel containing high-index oil and a ferrofluid plug. The switch is turned ON or OFF by movement of the ferrofluid plug. In contrast to conventional integrated switches, ferrofluid plugs act as switching mechanisms that are portable and reconfigurable. Switches are demonstrated in parallel geometries for single and multimode waveguides. Possible applications include optofluidic memory, multiplexed sensing for lab-on-chip, or frequency-encoded laser excitation. PMID:24514168

Gu, Yu; Valentino, Gianna; Mongeau, Eric

2014-02-01

185

Versatile ferrofluids based on polyethylene glycol coated iron oxide nanoparticles

NASA Astrophysics Data System (ADS)

Versatile ferrofluids based on polyethylene glycol coated iron oxide nanoparticles were obtained by a facile protocol and thoroughly characterized. Superparamagnetic iron oxide nanoparticles synthesized using a modified forced hydrolysis method were functionalized with polyethylene glycol silane (PEG silane), precipitated and dried. These functionalized particles are dispersable in a range of solvents and concentrations depending on the desired properties. Examples of tunable properties are magnetic behavior, optical and magneto-optical response, thermal features and rheological behavior. As such, PEG silane functionalized particles represent a platform for the development of new materials that have broad applicability in e.g. biomedical, industrial or photonic environments. Magnetic, optical, magneto-optical, thermal and rheological properties of several ferrofluids based on PEG coated particles with different concentrations of particles dispersed in low molecular mass polyethylene glycol were investigated, establishing the applicability of such materials.

Brullot, W.; Reddy, N. K.; Wouters, J.; Valev, V. K.; Goderis, B.; Vermant, J.; Verbiest, T.

2012-06-01

186

Condensation and ordering of colloidal spheres dispersed in a ferrofluid

NASA Astrophysics Data System (ADS)

Polystyrene microspheres of the same size dispersed in ferrofluid produce voids which have been denoted magnetic holes. The magnetic moment of one sphere (hole) is equal to the magnetic moment of the ferrofluid displaced by the sphere. The system may essentially be made two-dimensional by confining the dispersion between two glass plates with separation slightly larger than the sphere diameter. It is thus possible to have a model system of spheres with dipolar interactions which may be varied by external magnetic fields. Experimental studies to be discussed include aggregation of magnetic holes in external fields and the dynamics of magnetic holes in rotating external fields. The temporal evolution of the very complex trajectories are classified according to knot theory.

Skjeltorp, Arne T.

1995-02-01

187

Preparation of a biocompatible magnetic film from an aqueous ferrofluid

NASA Astrophysics Data System (ADS)

Very promising nanoparticles for biomedical applications or in medical drug targeting are superparamagnetic nanoparticles based on a core consisting of iron oxides (SPION) that can be targeted through external magnets. Polyvinyl alcohol (PVA) is a unique synthetic biocompatible polymer that can be chemically cross-linked to form a gel. Biotechnology applications of magnetic gels include biosensors, targeted drug delivery, artificial muscles and magnetic buckles. These gels are produced by incorporating magnetic materials in the polymer composites. In this paper we report the synthesis of an aqueous ferrofluid and the preparation of a biocompatible magnetic gel with polyvinyl alcohol and glutharaldehyde (GTA). HClO 4 was used to induce the peptization since this kind of ferrofluid does not have surfactant. The magnetic gel was dried to generate a biocompatible film.

Albornoz, Cecilia; Jacobo, Silvia E.

2006-10-01

188

Experimental investigation of a Brownian ratchet effect in ferrofluids

NASA Astrophysics Data System (ADS)

We test experimentally a Brownian ratchet system suggested by Engel [Phys. Rev. Lett. 91, 060602 (2003)]. This ratchet system is based on a magnetic fluid that contains nanometer sized magnetic particles in a thermal bath of carrier fluid. An external static magnetic field and, perpendicular to it, an oscillatory magnetic field act on the ferrofluid particles; the total magnetic field contains no rotating component. The directed effective rotation of the particles due to the ratchet effect induces a macroscopic torque density of the fluid. The torque on a spherical ferrofluid sample is measured in dependence on the field parameters. A quantitative comparison with predictions from a microscopic and a phenomenological model are given. Both models describe certain aspects of the measurements correctly, but qualitative discrepancies between both models and experiment are found, particularly in the high-frequency range.

John, Thomas; Stannarius, Ralf

2009-11-01

189

On the theory of the magnetoviscous effect in ferrofluids

The microscopic origin of viscoelastic effects in ferrofluids is studied theoretically. The growth kinetics of chain aggregates formed by magnetic ferroparticles under the action of the dipole-dipole interaction between them is analyzed. It is shown that the evolution rate for an ensemble of chains determines the rate of variation in the macroscopic stress of the medium upon a change in the applied external field and/or in the shear flow velocity. Consequently, the viscoelastic properties of magnetic fluids can be explained by the chain formation-destruction processes. The proposed microscopic model of a ferrofluid makes it possible (apparently, for the first time) to estimate the characteristic time of viscoelasticity corresponding to experimental results.

Zubarev, A. Yu., E-mail: andrey.zubarev@usu.ru; Chirikov, D. N. [Ural State University (Russian Federation)

2010-06-15

190

Raman spectroscopy on surfacted ferrofluids in a magnetic field.

We investigated the effect of an external magnetic field up to 0.25 T on the Raman spectra of surfacted ferrofluids with various magnetic-particle concentrations. With increasing magnetic field the Raman spectra, which display the characteristic broad bands associated with vibrations of surfactant and water molecules, show a pronounced decrease in intensity in the range up to 50 mT. We interpret this behavior as due to an increase of the local particle concentration in the magnetic fluid. At larger fields a magnetic excitation with an intensity growing in proportion to the magnetization of the ferrofluid becomes apparent at around 4400 cm(-1). We consider both effects as evidence for the formation of a solid structure by the magnetic nanoparticles in the presence of a magnetic field. PMID:12241178

Weber, J E; Goñi, A R; Pusiol, D J; Thomsen, C

2002-08-01

191

Floating oscillating-bodies constitute an important class of offshore wave energy converters. The testing of their power take-off equipment (PTO) (high-pressure hydraulics, linear electrical generator or other) under realistically simulated sea conditions is usually regarded as a major task. A laboratory rig, consisting of a U-tube enclosing an oscillating column of water driven by a time-varying air-pressure, was devised to simulate

A. F. de O. Falcão; P. E. R. Pereira; J. C. C. Henriques; L. M. C. Gato

2010-01-01

192

In this letter, dispersion properties of low-frequency electrostatic waves in multi-wall fullerene (the first layer is C60molecule) are investigated. It is assumed that multi-wall fullerene is charged due to the field emission, and hence the multi-wall fullerene can be regarded as charged dust spheres surrounded by degenerate electrons and ions. We obtain the dispersion relation for the low-frequency electrostatic oscillations

Ali Fathalian; Shahram Nikjo

2011-01-01

193

Magnetophoresis of ferrofluid in microchannel system and its nonlinear effect

We have studied the magnetophoretic particle separation and its nonlinear\\u000abehavior of ferrofluids in microchannel which is proposed by Furlani. The\\u000amagnetic gradient force is caused by an bias field and the polarized magnets\\u000aand is found to be spatially uniform in the channel section which can be used\\u000afor particle selecting or separation. We have derived the equations of

Y. C. Jian; L. F. Zhang; J. P. Huang

2006-01-01

194

Immunomagnetic cell separation, imaging, and analysis using Captivate ferrofluids

We have developed applications of CaptivateTM ferrofluids, paramagnetic particles (approximately 200 nm diameter), for isolating and analyzing cell populations in combination with fluorescence-based techniques. Using a microscope-mounted magnetic yoke and sample insertion chamber, fluorescent images of magnetically captured cells were obtained in culture media, buffer, or whole blood, while non-magnetically labeled cells sedimented to the bottom of the chamber. We

Laurie Jones; Joseph M. Beechem

2002-01-01

195

Cluster formation in ferrofluids induced by holographic optical tweezers.

Holographic optical tweezers were used to show the interaction between a strongly focused laser beam and magnetic nanoparticles in ferrofluid. When the light intensity was high enough, magnetic nanoparticles were removed from the beam center and formed a dark ring. The same behavior was observed when focusing vortex or Bessel beams. The interactions between two or more separated rings of magnetic nanoparticles created by independent optical traps were also observed. PMID:24081086

Masajada, Jan; Bacia, Marcin; Drobczy?ski, S?awomir

2013-10-01

196

Ferrofluid-based dispersive solid phase extraction of palladium.

A new mode of dispersive solid phase extraction based on ferrofluid has been developed. In this method, an appropriate amount of ferrofluid is injected rapidly into the aqueous sample by a syringe. Since the sorbent is highly dispersed in the aqueous phase, extraction can be achieved within a few seconds. The ferrofluid can be attracted by a magnet and no centrifugation step is needed for phase separation. Palladium was used as a model compound in the development and evaluation of the extraction procedure in combination with flame atomic absorption spectrometry. The experimental parameters (pH, DDTC concentration, type and concentration of eluent, the amount of adsorbent, extraction time, and the effect of interfering ions) were investigated in detail. Under the optimized conditions, the calibration graph was linear over the range of 1-100 ?g L(-1) and relative standard deviation of 3.3% at 0.1 ?g mL(-1) was obtained (n=7). The limit of detection and enrichment factor (EF) was obtained to be 0.35 ?g L(-1) and 267, respectively. The maximum adsorption capacity of the adsorbent at optimum conditions was found to be 24.6 mg g(-1) for Pd(II). The method was validated using certified reference material, and has been applied for the determination of trace Pd(II) in actual samples with satisfactory results. PMID:23618148

Farahani, Malihe Davudabadi; Shemirani, Farzaneh; Gharehbaghi, Maysam

2013-05-15

197

Accelerated thermal aging of petroleum-based ferrofluids

NASA Astrophysics Data System (ADS)

The effect of elevated temperature on the physical and insulating properties of ferrofluid specifically developed for use as a liquid dielectric (D-fluid) for power transformers has been investigated. The D-fluid was produced as a colloidal mix of a specifically synthesized ferrofluid with a conventional mineral oil, and it was subjected to thermal aging conditions modeled after a typical power transformer where the insulation fluid is expected to retain its dielectric performance for about 40 years of continuous service in a sealed tank. The well-known Arrhenius relationship was employed to model "life in service" for up to 40 years at 105°C which corresponded to holding the samples in sealed jars for 10 weeks at 185°C. Another set of small ampules (5 ml) was prepared to test the main physical properties after even longer aging. D-fluid tested after a period of 34 and 50 weeks at 185°C showed no degradation of thermal or colloid stability. The dielectric colloid was also subjected to a 21 day-long test at 110°C in a sealed jar in the presence of typical transformer materials: copper, cellulose, and silicon steel (so-called "bomb" test). Finally, the ferrofluid went through an oxidation stability test (ASTM D2440). Test results show that the newly developed dielectric colloid satisfies the long-term service requirements the transformer users typically apply to conventional mineral oils.

Segal, V.; Nattrass, D.; Raj, K.; Leonard, D.

1999-07-01

198

Deformation and Magnetophoresis of Bubbles in Magnetic Fluids (Ferrofluids)

NASA Astrophysics Data System (ADS)

The deformation and coalescence of small bubbles in magnetic fluid (ferrofluid) are directly observed and measured using a novel X-ray phase contrast imaging technique. High resolution X-ray images and videos of water-based ferrofluid (EMG-607/707) reveal: (i) vapor bubbles having diameters in the range 50 to 1000 microns form readily, (ii) neighboring bubbles chain together readily, but do not merge, and (iii) the dynamics of interfaces (bubbles) in ferrofluids are modified by the presence of long chain-like aggregates of the constituent magnetic nanoparticles. Isolated bubbles larger than a few hundred microns become visibly prolate in an applied field, elongating along the field direction. The observed deformations compare favorably with theoretical estimates and the results of direct numerical simulations (DNS). Coalescence is driven by attractive magnetophoretic force induced by non-uniform fields associated with individual bubbles, as was verified by comparing coalescence dynamics to theoretical prediction and to detailed results from DNS. Chain like aggregates of magnetic nanoparticles aligned with the applied field were ubiquitous and led to anisotropic field dependent drag effects. A multiple color function Volume of Fluid (VOF) technique was used to suppress bubble merger in DNS.

Yecko, Philip; Lee, Wah-Keat; Scardovelli, Ruben; Trubatch, A. David

2009-11-01

199

Disclosed are processes for monitoring and control of underground contamination, which involve the application of ferrofluids. Two broad uses of ferrofluids are described: (1) to control liquid movement by the application of strong external magnetic fields; and (2) to image liquids by standard geophysical methods.

Moridis, George J. (Oakland, CA); Oldenburg, Curtis M. (Mill Valley, CA)

2001-01-01

200

Enhancement of the field modulation of light transmission through films of binary ferrofluids.

CoFe2O4 nanoparticles are ferrimagnetic and p-MgFe2O4 nanoparticles are paramagnetic. Binary ferrofluids can be synthesized by mixing CoFe2O4 ferrofluids and p-MgFe2O4 fluids in such a way that the magnetic interaction of the CoFe2O4 particles is large enough to form field-induced chainlike aggregates. The field modulation of light transmission through films of CoFe{2}O{4}-p-MgFe2O4 binary ferrofluids with different values of applied magnetic field is compared with pure CoFe2O4 ferrofluids. The experimental results revealed that the light transmission coefficient of binary ferrofluids can be more intensely modulated by an external magnetic field than pure CoFe2O4 ferrofluids. These show that in the binary ferrofluids, the field-induced structure mainly arises from the CoFe2O4 nanoparticle system and the p-MgFe2O4 nanoparticles introduce a nonlinear modulation effect, even though the microstructure of p-MgFe2O4 fluids is not affected by an applied magnetic field. Using a model of magnetic bidispersal, the enhanced field modulation of the light transmission through binary ferrofluids is explained by the coupling of geometric shadowing effects from both the CoFe2O4 and p-MgFe2O4 particle systems. PMID:20866805

Zhang, Ting-Zhen; Li, Jian; Miao, Hua; Zhang, Qing-Mei; Fu, Jun; Wen, Bang-Cai

2010-08-01

201

NASA Astrophysics Data System (ADS)

The main aim of this lecture is to provide a broad overview of the area of hydrodynamic simulation. The provision of introductions to a couple of basic algorithms for solving the equations of gas dynamics is a secondary objective. Hydrodynamic simulation in the context of laser-plasma physics and inertial fusion is now a large and mature field, deserving of an entire book (or books…) for a proper treatment. Individual topics will not be treated in great depth, and mathematical detail is avoided where possible. It is hoped that the reader will understand the key aspects of hydrodynamic simulation and the ability to write a very simple 1D hydro-solver with a view to using this knowledge as a "springboard" for more in-depth study.

Robinson, Alex P. L.

202

Preparation of a novel ferrofluidic photoresist for two-photon photopolymerization technique

NASA Astrophysics Data System (ADS)

We present a novel route for the preparation of ferrofluidic photoresist compatible with two-photon photopolymerization (TPP). To get a homogeneous ferrofluidic photoresit, the compatibility of photoresist and magnetic materials has been improved. Monodispersed Fe3O4 nanoparticles synthesized via thermal decomposition of iron precursor were stabilized by 6-(methacryloyloxy) hexanoic acid (a kind of acrylate-based monomer). A ferrofluidic photoresist was prepared by doping the modified Fe3O4 nanoparticles in acrylate-based resin. In this way, the dispersibility of nanoparticles in photoresist was enhanced significantly. As a representative example, a precise magnetic micron-sized spring was created. In the test of the magnetic response, the sensitivity of magnetic microspring was improved remarkably due to the optimization of the ferrofluidic photoresist. When the intensity of external magnetic field reached a value of 1500 Gs, the deformation rate of the microspring would get to 2.25, indicating the compatibility of the ferrofluidic photoresist in microfabrication.

Tian, Ye; Lu, Dongxiao; Jiang, Haobo; Lin, Xiaomei

2012-10-01

203

ERIC Educational Resources Information Center

Explores in a non-mathematical treatment some of the hydrodynamical phenomena and forces that affect the operation of ships, especially at high speeds. Discusses the major components of ship resistance such as the different types of drags and ways to reduce them and how to apply those principles for the hovercraft. (GA)

Lafrance, Pierre

1978-01-01

204

National Technical Information Service (NTIS)

This document is the final report for AFOSR Grant F49620-99-1-0070, 'Lattice Hydrodynamics'. Under the terms of this grant, the Center for Computational Science at Boston University provided theoretical and computational support to the Lattice-Gas Theory ...

B. M. Boghosian

2001-01-01

205

Supersonic flow past bodies in dispersive hydrodynamics

The problem of steady two-dimensional supersonic flow about slender pointed bodies is studied in dispersive hydrodynamics. The equivalence of this problem to the Gurevich-Pitaevskii evolutionary problem of dissipationless shock waves in Korteweg-de Vries hydrodynamics is shown. The Whitham technique is used to derive a number of exact solutions describing different cases of flow around objects in dispersive hydrodynamics. 22 refs., 7 figs.

Gurevich, A.V. [P.N. Lebedev Inst., Moscow (Russian Federation); Krylov, A.L.; Khodorovskii, V.V. [O.Yu Schmidt Inst. of Earth Physics, Moscow (Russian Federation)] [and others

1995-07-01

206

We present a detailed theoretical analysis of the gravitational wave (GW) signal of the post-bounce evolution of core-collapse supernovae (SNe), employing for the first time relativistic, two-dimensional explosion models with multi-group, three-flavor neutrino transport based on the ray-by-ray-plus approximation. The waveforms reflect the accelerated mass motions associated with the characteristic evolutionary stages that were also identified in previous works: a quasi-periodic modulation by prompt post-shock convection is followed by a phase of relative quiescence before growing amplitudes signal violent hydrodynamical activity due to convection and the standing accretion shock instability during the accretion period of the stalled shock. Finally, a high-frequency, low-amplitude variation from proto-neutron star (PNS) convection below the neutrinosphere appears superimposed on the low-frequency trend associated with the aspherical expansion of the SN shock after the onset of the explosion. Relativistic effects in combination with detailed neutrino transport are shown to be essential for quantitative predictions of the GW frequency evolution and energy spectrum, because they determine the structure of the PNS surface layer and its characteristic g-mode frequency. Burst-like high-frequency activity phases, correlated with sudden luminosity increase and spectral hardening of electron (anti-)neutrino emission for some 10 ms, are discovered as new features after the onset of the explosion. They correspond to intermittent episodes of anisotropic accretion by the PNS in the case of fallback SNe. We find stronger signals for more massive progenitors with large accretion rates. The typical frequencies are higher for massive PNSs, though the time-integrated spectrum also strongly depends on the model dynamics.

Mueller, Bernhard; Janka, Hans-Thomas; Marek, Andreas, E-mail: bjmuellr@mpa-garching.mpg.de, E-mail: thj@mpa-garching.mpg.de, E-mail: amarek@mpa-garching.mpg.de [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany)] [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany)

2013-03-20

207

NASA Astrophysics Data System (ADS)

We present a detailed theoretical analysis of the gravitational wave (GW) signal of the post-bounce evolution of core-collapse supernovae (SNe), employing for the first time relativistic, two-dimensional explosion models with multi-group, three-flavor neutrino transport based on the ray-by-ray-plus approximation. The waveforms reflect the accelerated mass motions associated with the characteristic evolutionary stages that were also identified in previous works: a quasi-periodic modulation by prompt post-shock convection is followed by a phase of relative quiescence before growing amplitudes signal violent hydrodynamical activity due to convection and the standing accretion shock instability during the accretion period of the stalled shock. Finally, a high-frequency, low-amplitude variation from proto-neutron star (PNS) convection below the neutrinosphere appears superimposed on the low-frequency trend associated with the aspherical expansion of the SN shock after the onset of the explosion. Relativistic effects in combination with detailed neutrino transport are shown to be essential for quantitative predictions of the GW frequency evolution and energy spectrum, because they determine the structure of the PNS surface layer and its characteristic g-mode frequency. Burst-like high-frequency activity phases, correlated with sudden luminosity increase and spectral hardening of electron (anti-)neutrino emission for some 10 ms, are discovered as new features after the onset of the explosion. They correspond to intermittent episodes of anisotropic accretion by the PNS in the case of fallback SNe. We find stronger signals for more massive progenitors with large accretion rates. The typical frequencies are higher for massive PNSs, though the time-integrated spectrum also strongly depends on the model dynamics.

Müller, Bernhard; Janka, Hans-Thomas; Marek, Andreas

2013-03-01

208

Mössbauer spectroscopic characterization of manganese and cobalt ferrite ferrofluids

NASA Astrophysics Data System (ADS)

Aqueous ferrofluids based on Mn and Co ferrites have been synthesized by a novel method. Mössbauer spectra of dried samples (average particle diameter ? 10 nm) were measured in the 77 340 K temperature range. CoFe2O4 spectra show no superparamagnetic (SP) relaxation, in accordance with the high magnetic anisotropy of this compound. MnFe2O4 spectra exhibit SP relaxation, from which an effective K=(8±3)×104 J/m3 is estimated. This value represents a 20× enhancement over intrinsic magnetocrystalline anisotropy.

Rechenberg, H. R.; Tourinho, F. A.

1991-11-01

209

Label-free cellular manipulation and sorting via biocompatible ferrofluids

We present a simple microfluidic platform that uses biocompatible ferrofluids for the controlled manipulation and rapid separation of both microparticles and live cells. This low-cost platform exploits differences in particle size, shape, and elasticity to achieve rapid and efficient separation. Using microspheres, we demonstrate size-based separation with 99% separation efficiency and sub-10-?m resolution in <45 s. We also show continuous manipulation and shape-based separation of live red blood cells from sickle cells and bacteria. These initial demonstrations reveal the potential of ferromicrofluidics in significantly reducing incubation times and increasing diagnostic sensitivity in cellular assays through rapid separation and delivery of target cells to sensor arrays.

Kose, Ayse R.; Fischer, Birgit; Mao, Leidong; Koser, Hur

2009-01-01

210

Scattering from dilute ferrofluid suspensions in soft polymer gels.

Small angle neutron and x-ray scattering methods are used to investigate the structure of dilute suspensions of two different ferrofluid systems dispersed in soft polyacrylamide hydrogels. It is found that the particles in the fluid are fractal aggregates composed of smaller particles of radius ca. 5 nm. The fractal dimension is strongly dependent on sample, taking the value 1.7 in the first sample and 2.9 in the second sample. In the presence of a magnetic field the aggregates orient, but are restricted in both their translational and rotational freedom. The effect of the gel elasticity is treated as a hindrance to the orientation process. PMID:12636681

Teixeira, Alvaro V; Morfin, Isabelle; Ehrburger-Dolle, Françoise; Rochas, Cyrille; Geissler, Erik; Licinio, Pedro; Panine, Pierre

2003-02-01

211

NASA Astrophysics Data System (ADS)

We present a study on the development of the cellulosolytic fungi Chaetomium globosum Kunze:Fr. under the influence of a petroleum ferrofluid, added at various concentrations to the culture medium. A positive influence of the ferrofluid was revealed at the level of the growth rate during the first week of the experiment. Further, the biomass accumulation rate was diminished in the sample in comparison to the control without the addition of ferrofluid. The ubiquitous capacity of the fungi for iron internalization under the form of complex combinations known as siderophores, is probably related to the observed behavior of Chaetomium globosum Kunze:Fr.

Manoliu, Al.; Antohe, Lacramioara; Creanga, Dorina E.; Cotae, C.

1999-07-01

212

NASA Astrophysics Data System (ADS)

The small-sized herringbone groove journal bearing (HGJB), i.e., so-called ``magnetic bearing,'' filled with Newtonian ferrofluid lubrication is investigated via finite difference analysis (FDA), with consideration of cavitation zones in HGJB. The FDA starts with constructing the mass flux equations of the HGJB filled with ferrofluid. Discretization for FDA is next performed over the bearing clearance domain, from which algebraic finite difference equations based on the mass flow balance over the clearance domain are derived. Solving the equations, rotordynamic coefficients, cavitation zones, and side leakage rate are successfully predicted to show effectiveness in enhancing bearing performance by ferrofluid.

Kao, Yung-Yuan; Chao, Paul C.-P.; Liu, Zong-Bin; Wang, Zhi-Kuan; Liu, Po-Wen; Huang, Jeng-Shen; Chang, Chang-Chun

2009-04-01

213

Enhanced separation of magnetic and diamagnetic particles in a dilute ferrofluid

NASA Astrophysics Data System (ADS)

Traditional magnetic field-induced particle separations take place in water-based diamagnetic solutions, where magnetic particles are captured while diamagnetic particles flow through without being affected by the magnetic field. We demonstrate that replacing the diamagnetic aqueous medium with a dilute ferrofluid can significantly increase the throughput of magnetic and diamagnetic particle separation. This enhancement is attributed to the simultaneous positive and negative magnetophoresis of magnetic and diamagnetic particles, respectively, in a ferrofluid. The particle transport behaviors in both ferrofluid- and water-based separations are predicted using an analytical model.

Liang, Litao; Zhang, Cheng; Xuan, Xiangchun

2013-06-01

214

Process for decontaminating radioactive waste water using a ferrofluid and magnetic separation

The present invention provides a process for decontaminating radioactive waste water containing a radioactive element that forms a water-insoluble compound. This process includes the steps of forming the compound of the radioactive element, treating the resulting waste water with a ferrofluid, dispersing the ferrofluid, diluting the solids concentration of the resulting mixture with a coagulation initiator, such as ethyl alcohol or acetone, and collecting by use of a magnetic field, the resulting radioactive sludge. In a variation of the process, the steps involving the use of the coagulation initiator and the use of the ferrofluid are reversed.

Silver, G.L.

1980-07-31

215

Use of a ferrofluid as the heat-exchange fluid in a magnetic refrigerator

The use of a ferrofluid is proposed as the heat-exchange fluid in a wheel-type magnetic refrigerator in order to avoid flow-control problems. An equivalent-circuit analysis of the ferrofluid flow path with several different magnetic field profiles indicates that it is possible to obtain the desired flow control in at least one case. Sample design calculations for the revised wheel-type refrigerator are presented. In addition, the results of heat-transfer measurements from kerosene to a stainless-steel screen and from a kerosene-base ferrofluid to the same screen in and out of an 8-T magnetic field are described.

Barclay, J.A.

1982-04-01

216

Density separation of solids in ferrofluids with magnetic grids

Nonmagnetic solids in a superparamagnetic ferrofluid are subjected to body forces proportional to the intensity of magnetization of the fluid and the gradient of the magnetic field. An apparent density of the fluid can be defined from the force equations, and since the apparent density can be much larger than the true density, it is possible to levitate or float dense objects. Mixtures of solids with a density greater than the apparent density sink while lower density solids float. In practice it is difficult to create a uniform gradient over a large volume and single gap magnetic separators require very large magnets or have a limited throughput. To overcome that problem, multiple gap magnetic grids have been designed. Such grids consist of planar arrays of parallel bars of alternating polarity, driven by permanent magnets. When immersed in ferrofluid, magnetic grids create nonuniform field gradients and apparent densities in the fluid. However, both analysis and experimental measurements show that the grid acts as a barrier to particles below a critical density, while permitting more dense particles to fall through the grid. Thus, a magnetic grid filter can be used as a high throughput binary separator of solids according to their densities. Such filters can be cascaded for more complex separations. Several magnetic grid filters have been designed, built, and tested. Magnetic measurements qualitatively agree with the theoretical predictions. Experiments with synthetic mixtures have demonstrated that good binary separations can be made.

Fay, H. (Union Carbide Corp., Tonawanda, NY); Quets, J.M.

1980-04-01

217

A comparative study of different ferrofluid constitutive equations.

NASA Astrophysics Data System (ADS)

Ferrofluids are stable colloidal suspensions of fine ferromagnetic monodomain nanoparticles in a non-conducting carrier fluid.The particles are coated with a surfacant to avoid agglomeration and coagulation.Brownian motion keeps the nanoparticles from settling under gravity.In recent years these fluids have found several applications including in liquid seals in rotary shafts for vacuum system and in hard disk drives of personal computers,in cooling and damping of loud speakers, in shock absorbers and in biomedical applications. A continuum description of ferrofluids was initiated by Neuringer and Rosensweig [1] but the theory had some limitations. In subsequent years,several authors have proposed generalization of the above theory.Some of these are based upon the internal particle rotation concept, some are phemonological,some are based upon a thermodynamic framework,some employ statistical approach and some have used the dynamic mean field approach.The results based upon these theories ane in early stages and inconclusive. Our purpose is, first, to critically examine the basic foundations of these equations and then study the pedictions obtained in all the theories related to an experimental as well as a theoretical study. [1]J.L.Neuringer and R.E. Rosensweig, Physics Fluids,7.1727 (1964)..

Kaloni, Purna

2011-11-01

218

Exploiting magnetic asymmetry to concentrate diamagnetic particles in ferrofluid microflows

NASA Astrophysics Data System (ADS)

Concentrating particles and cells for measurement or removal is often essential in many chemical and biological applications. Diamagnetic particle concentration has been demonstrated in magnetic fluids using two repulsive or attracting magnets, which in almost all cases are symmetrically positioned on the two sides of the particle-flowing channel. This work studies the effects of magnet asymmetry on the pattern and flow rate of diamagnetic particle concentration in ferrofluid flow through a straight rectangular microchannel. Two attracting permanent magnets with a fixed distance are each embedded on one side of the microchannel with a symmetric or an asymmetric configuration. A pair of symmetric counter-rotating circulations of concentrated particles is formed in the microchannel with a symmetric magnet configuration, which is found to grow in size and progress up the flow. In contrast, the single asymmetric circulation of concentrated particles formed in the microchannel with an asymmetric magnet configuration nearly maintains its size and position. Moreover, the magnet asymmetry is found to increase the ferrofluid flow rate for particle trapping, which is predicted by a three-dimensional theoretical model with a reasonable agreement.

Wilbanks, James J.; Kiessling, Garrett; Zeng, Jian; Zhang, Cheng; Tzeng, Tzuen-Rong; Xuan, Xiangchun

2014-01-01

219

NASA Astrophysics Data System (ADS)

We construct the hydrodynamics of quantum critical points with Lifshitz scaling. There are new dissipative effects allowed by the lack of boost invariance. The formulation is applicable, in general, to any fluid with an explicit breaking of boost symmetry. We use a Drude model of a strange metal to study the physical effects of the new transport coefficient. It can be measured using electric fields with non-zero gradients, or via the heat production when an external force is turned on. The resistivity is proportional to the drag coefficient, scaling arguments fix it to be linear in the temperature.

Hoyos, Carlos; Kim, Bom Soo; Oz, Yaron

2013-11-01

220

Graphene oxide/ferrofluid/cement composites for electromagnetic interference shielding application.

This paper deals with the preparation of graphene oxide-ferrofluid-cement nanocomposites to evaluate the electromagnetic interference (EMI) shielding effectiveness (SE) in the 8.2-12.4 GHz frequency range. It has been observed that incorporation of graphene oxide (30 wt%) along with an appropriate amount of ferrofluid in the cement matrix leads to a shielding effectiveness of 46 dB (>99% attenuation).The presence of graphene oxide and ferrofluid in the cement leads to strong polarizations and magnetic losses that consequently result in higher shielding effectiveness compared to pristine cement. The resulting nanocomposites have shown Shore hardness of 54 and dc conductivity of 10.40 S cm( - 1). SEM reveals the homogeneous dispersion of graphene oxide and ferrofluid in the cement matrix. PMID:22024967

Singh, Avanish Pratap; Mishra, Monika; Chandra, Amita; Dhawan, S K

2011-11-18

221

Nonlinear deformation of a ferrofluid droplet in a uniform magnetic field.

This paper reports experimental and numerical results of the deformation of a ferrofluid droplet on a superhydrophobic surface under the effect of a uniform magnetic field. A water-based ferrofluid droplet surrounded by immiscible mineral oil was stretched by a magnetic field parallel to the substrate surface. The results show that an increasing flux density increases the droplet width and decreases the droplet height. A numerical model was established to study the equilibrium shape of the ferrofluid droplet. The governing equations for physical fields, including the magnetic field, are solved by the finite volume method. The interface between the two immiscible liquids was tracked by the level-set method. Nonlinear magnetization was implemented in the model. Comparison between experimental and numerical results shows that the numerical model can predict well the nonlinear deformation of a ferrofluid droplet in a uniform magnetic field. PMID:22044246

Zhu, Gui-Ping; Nguyen, Nam-Trung; Ramanujan, R V; Huang, Xiao-Yang

2011-12-20

222

Preparation and characterization of thermal-sensitive ferrofluids for drug delivery application

NASA Astrophysics Data System (ADS)

Novel thermal-sensitive ferrofluids (F127-ferrofluids) consisting of core-shell-type magnetic nanoparticles dispersed in Pluronic F127-containing aqueous solution were prepared. The core (magnet)-shell (Pluronic F127) nanoparticles were synthesized by in situ co-precipitation process, which were characterized using transmission electron microscope, X-ray diffraction and vibrating sample magnetometer. The F127-ferrofluids gelled above the lower critical solution temperatures (LCST) of approximately 23-28 °C, which were higher than that of pure Pluronic F127-fluids (21-25 °C). The increase in the LCST of the F127 ferrofluids may be attributed to a result of a physical interaction between the F127 molecules and the core-shell magnetic nanoparticles.

Liu, Ting-Yu; Hu, Shang-Hsiu; Hu, Sheng-Hsiang; Tsai, Szu-Ping; Chen, San-Yuan

2007-03-01

223

Effect of an alternating nonuniform magnetic field on ferrofluid flow and heat transfer in a channel

NASA Astrophysics Data System (ADS)

Forced convective heat transfer of water based Fe3O4 nanofluid (ferrofluid) in the presence of an alternating non-uniform magnetic field is investigated numerically. The geometry is a two-dimensional channel which is subjected to a uniform heat flux at the top and bottom surfaces. Nonuniform magnetic field produced by eight line source dipoles is imposed on several parts of the channel. Also, a rectangular wave function is applied to the dipoles in order to turn them on and off alternatingly. The effects of the alternating magnetic field strength and frequency on the convective heat transfer are investigated for four different Reynolds numbers (Re=100, 600, 1200 and 2000) in the laminar flow regime. Comparing the results with zero magnetic field case, show that the heat transfer enhancement increases with the Reynolds number and reaches a maximum of 13.9% at Re=2000 and f=20 Hz. Moreover, at a constant Reynolds number, it increases with the magnetic field intensity while an optimum value exists for the frequency. Also, the optimum frequency increases with the Reynolds number. On the other hand, the heat transfer enhancement due to the magnetic field is always accompanied by a pressure drop penalty. A maximum pressure drop increase of 6% is observed at Re=2000 and f=5 Hz which shows that the pressure drop increase is not as significant as the heat transfer enhancement.

Goharkhah, Mohammad; Ashjaee, Mehdi

2014-08-01

224

Motion of a droplet on a planar surface has applications in droplet-based lab on a chip technology. This paper reports the experimental results of the shape, contact angles, and motion of ferrofluid droplets driven by a permanent magnet on a planar homogeneous surface. The water-based ferrofluid in use is a colloidal suspension of single-domain magnetic nanoparticles. The effect of the magnetic field on the apparent contact angle of the ferrofluid droplet was first investigated. The results show that an increasing magnetic flux decreases the apparent contact angle of a sessile ferrofluid droplet. Next, the dynamic contact angle was investigated by observing the shape and the motion of a sessile ferrofluid droplet. The advancing and receding contact angles of the moving ferrofluid were measured at different moving speeds and magnetic field strengths. The measured contact angles were used to estimate the magnitude of the forces involved in the sliding motion. Scaling analysis was carried out to derive the critical velocity, beyond which the droplet is not able to catch up with the moving magnet. PMID:20608704

Nguyen, Nam-Trung; Zhu, Guiping; Chua, Yong-Chin; Phan, Vinh-Nguyen; Tan, Say-Hwa

2010-08-01

225

Particle size distribution in ferrofluid macro-clusters

NASA Astrophysics Data System (ADS)

Under an applied magnetic field, many commercial and concentrated ferrofluids agglomerate and form large micron-sized structures. Although large diameter particles have been implicated in the formation of these macro-clusters, the question of whether the particle size distribution of the macro-clusters are the same as the original fluid remains open. Some studies suggest that these macro-clusters consist of larger particles, while others have shown that there is no difference in the particle size distribution between the macro-clusters and the original fluid. In this study, we use X-ray imaging to aid in a sample (diluted EFH-1 from Ferrotec) separation process and conclusively show that the average particle size in the macro-clusters is significantly larger than those in the original sample. The average particle size in the macro-clusters is 19.6 nm while the average particle size of the original fluid is 11.6 nm.

Lee, Wah-Keat; Ilavsky, Jan

2013-03-01

226

Magnetocoalescence of ferrofluid droplets in a flat microfluidic channel

NASA Astrophysics Data System (ADS)

In this work we present the numerical study of the deformation and the coalescence of two ferrofluid droplets in a uniform applied magnetic field. Employing the boundary element method (BEM), we numerically solve the Darcy equation in a flat microfluidic channel by applying the magnetic normal stress as a boundary condition at the interfaces of droplets. The occurrence of different numerical regimes is summarized in the two phase diagrams scanned by the distance between two droplets, magnetic capillary number, and magnetic permeability. We also show the existence of the critical separation of two droplets where the coalescence of the droplets is inhibited. This critical value is independent of the applied-magnetic-field intensity, although it depends on the permeability ratio of droplet and continuous phase.

Kadivar, Erfan

2014-04-01

227

Ferrofluidic torsional pendulum driven by oscillating magnetic field.

A thin disk-shaped container filled with a ferrofluid and suspended in a horizontal linearly polarized ac magnetic field can perform torsional vibrations around its vertical diameter. In contrast to a recently studied spherical pendulum, the cell is sensitive to the field direction: It exposes its edge to the stationary or slowly oscillating magnetic field, and its broad side to the field of a high frequency. When the amplitude of the latter field is increased, the state of rest gets destabilized, yielding to oscillations near the equilibrium. Further growth of the field strength results in the onset of the cell rotation. We describe sequences of local and global bifurcations which accompany those transitions. PMID:16906947

Shliomis, Mark I; Zaks, Michael A

2006-06-01

228

Relaxation mechanisms of photoinduced periodic microstructures in ferrofluid layers.

We consider theoretically and numerically a periodic concentration grating induced in a layer of ferrofluid in the presence of the external magnetic field by nonuniform optical heating through photoabsorption. The stationary profiles of the periodic microstructures are governed by the equilibrium of the diffusive, thermodiffusive, and magnetic fluxes. The anisotropy of the diffusion coefficient and the magnetically driven microconvection contribute to the relaxation of these structures. The temperature-concentration coupling is shown to increase the initial effective diffusive relaxation rate by up to 50%. Microconvection dominates in the relaxation process even at small values of the control parameter and rapidly destroys the periodic part of the concentration grating. We describe this process in the weakly nonlinear regime by an approximate Galerkin model. PMID:22304188

Zablotsky, Dmitry; Blums, Elmars

2011-12-01

229

Field-induced structure of confined ferrofluid emulsion

Field-induced phase behavior of a confined monodisperse ferrofluid emulsion was studied using optical microscopy, light transmission, and static light scattering techniques. Upon application of magnetic field, randomly-dispersed magnetic emulsion droplets form solid structures at [lambda] = 1.5, where [lambda] is defines as the ratio of the dipole-dipole interaction energy to the thermal energy at room temperature. The new solid phase consists of either single droplet chains, columns, or worm-like clusters, depending on the volume fraction, cell thickness and rate of field application. For the column phase, an equilibrium structure of equally-sized and spaced columns was observed. The measurements taken for cell thickness 5[mu]m [<=] L [<=] 500 [mu]m and volume fraction 0.04 show the column spacing to be reasonably described by d = 1.49 L[sup 0.34].

Lawrence, E.M.; Ivey, M.L.; Flores, G.A.; Liu, J. (California State Univ., Long Beach, CA (United States). Dept. of Physics and Astronomy); Bibette, J. (Centre de Recherche Paul Pascal, Pessac (France)); Richard, J. (Rhone-Poulenc Recherches, Aubervilliers (France))

1994-09-01

230

Hydrodynamic instabilities in astrophysics and in laboratory high-energy–density systems

High-energy–density systems and astrophysical systems both involve hydrodynamic effects, including sources of pressure, shock waves, rarefactions and plasma flows. In the evolution of such systems, hydrodynamic instabilities naturally evolve. As a result, a fundamental understanding of hydrodynamic instabilities is necessary to understand their behaviour. This paper discusses the validity of a hydrodynamic description in both cases, and, from the common

R P Drake

2005-01-01

231

Following recent observations of large scale correlated motion of chromatin inside the nuclei of live differentiated cells, we present a hydrodynamic theory-the two-fluid model-in which the content of a nucleus is described as a chromatin solution with the nucleoplasm playing the role of the solvent and the chromatin fiber that of a solute. This system is subject to both passive thermal fluctuations and active scalar and vector events that are associated with free energy consumption, such as ATP hydrolysis. Scalar events drive the longitudinal viscoelastic modes (where the chromatin fiber moves relative to the solvent) while vector events generate the transverse modes (where the chromatin fiber moves together with the solvent). Using linear response methods, we derive explicit expressions for the response functions that connect the chromatin density and velocity correlation functions to the corresponding correlation functions of the active sources and the complex viscoelastic moduli of the chromatin solution. We then derive general expressions for the flow spectral density of the chromatin velocity field. We use the theory to analyze experimental results recently obtained by one of the present authors and her co-workers. We find that the time dependence of the experimental data for both native and ATP-depleted chromatin can be well-fitted using a simple model-the Maxwell fluid-for the complex modulus, although there is some discrepancy in terms of the wavevector dependence. Thermal fluctuations of ATP-depleted cells are predominantly longitudinal. ATP-active cells exhibit intense transverse long wavelength velocity fluctuations driven by force dipoles. Fluctuations with wavenumbers larger than a few inverse microns are dominated by concentration fluctuations with the same spectrum as thermal fluctuations but with increased intensity. PMID:24806919

Bruinsma, Robijn; Grosberg, Alexander Y; Rabin, Yitzhak; Zidovska, Alexandra

2014-05-01

232

Interfacial stress balances in structured continua and free surface flows in ferrofluids

NASA Astrophysics Data System (ADS)

Interfacial linear and internal angular momentum balances are obtained for a structured continuum and for the special case of a ferrofluid, a suspension of magnetic nanoparticles in a Newtonian fluid. The interfacial balance equations account for the effects of surface tension and surface tension gradient, magnetic surface excess forces, antisymmetric stresses, and couple stresses in driving interfacial flows in ferrofluids. Application of the interfacial balance equations is illustrated by obtaining analytical expressions for the translational and spin velocity profiles in a thin film of ferrofluid on an infinite flat plate when a rotating magnetic field is applied with axis of rotation parallel to the ferrofluid/air interface. The cases of zero and non-zero spin viscosity are considered for small applied magnetic field amplitude. Expressions for the maximum translational velocity, slope of the translational velocity profile at the ferrofluid/air interface, and volumetric flow rate are obtained and their use to test the relevance of spin viscosity and couple stresses in the flow situation under consideration is discussed.

Chaves, Arlex; Rinaldi, Carlos

2014-04-01

233

Field-induced structures in miscible ferrofluid suspensions with and without latex spheres.

We explore magnetic-field-induced ordering and microphase separation of aqueous ferrofluid and of aqueous mixtures of ferrofluid with nonmagnetic latex spheres. The ferrofluid is a surfactant stabilized aqueous suspension of magnetite (Fe3O4) particles with average diameter 20 nm (including the approximately 2.5-nm thick surfactant layer); the nonmagnetic latex spheres are charge stabilized polymethylmethacrylate (PMMA) particles with diameters of 42 nm, 108 nm, and 220 nm. In the presence of a uniform magnetic field, needlelike ferrofluid droplets formed that eventually grew to sample-traversing columns at fields of approximately 600 G; the two-dimensional structure of these columns was, however, glassy rather than hexagonal. In higher fields, approximately 1000 G, the columns stretched and coalesced into sheetlike striped liquids, but a true lamellar phase was not observed. The addition of nonmagnetic latex spheres to the ferrofluid suspension lowered substantially the critical field for the formation of columns, and induced lamellar (stripe) phases at relatively low applied fields. Image analysis was used to determine the spatial correlation functions, the average needle or column spacing, and the average lamellae spacing of these samples as a function of latex sphere size and concentration. PMID:12636674

Islam, M F; Lin, K H; Lacoste, D; Lubensky, T C; Yodh, A G

2003-02-01

234

Any single permanent or electro magnet will always attract a magnetic fluid. For this reason it is difficult to precisely position and manipulate ferrofluid at a distance from magnets. We develop and experimentally demonstrate optimal (minimum electrical power) 2-dimensional manipulation of a single droplet of ferrofluid by feedback control of 4 external electromagnets. The control algorithm we have developed takes into account, and is explicitly designed for, the nonlinear (fast decay in space, quadratic in magnet strength) nature of how the magnets actuate the ferrofluid, and it also corrects for electro-magnet charging time delays. With this control, we show that dynamic actuation of electro-magnets held outside a domain can be used to position a droplet of ferrofluid to any desired location and steer it along any desired path within that domain – an example of precision control of a ferrofluid by magnets acting at a distance.

Probst, R.; Lin, J.; Komaee, A.; Nacev, A.; Cummins, Z.

2010-01-01

235

NASA Astrophysics Data System (ADS)

Using a ferrofluid of cobalt-zinc ferrite nanoparticles (Co0.8Zn0.2Fe2O4) coated with oleic acid and suspended in ethanol, we have fabricated a 2D photonic crystal (PC) by the application of an external magnetic field perpendicular to the plane of the ferrofluid. The 2D PC is made by rods of nanoparticles organized in a hexagonal structure. By means of the plane-wave expansion method, we study its photonic band structure (PBS) which depends on the effective permittivity and on the area ratio of the liquid phase. Additionaly, taking into account the Maxwell-Garnett theory we calculated the effective permittivity of the rods. We have found that the effective refractive index of the ferrofluid increases with its magnetization. Using these results we calculate the band structure of the photonic crystal at different applied magnetic fields, finding that the increase of the applied magnetic field shifts the band structure to lower frequencies with the appearance of more band gaps.

López, J.; González, Luz E.; Quiñonez, M. F.; Porras-Montenegro, N.; Zambrano, G.; Gómez, M. E.

2014-04-01

236

NASA Astrophysics Data System (ADS)

Ferrofluids based on magnetic Co0.25Zn0.75Fe2O4 ferrite nanoparticles were prepared by co-precipitation method from aqueous salt solutions of Co (II), ZnSO4, and Fe (III) in an alkaline medium. Ferrofluids placed in an external magnetic field show properties that make them interesting as magneto-controllable soft photonic crystals. Morphological and structural characterizations of the samples were obtained from Scanning Electron Microscopy and Transmission Electron Microscopy studies. Magnetic properties were investigated with the aid of a vibrating sample magnetometer at room temperature. Herein, the Co0.25Zn0.75Fe2O4 samples showed superparamagnetic behavior, according to hysteresis loop results. Taking in mind that the Co-Zn ferrite hysteresis loop is very small, our magnetic nanoparticles can be considered soft magnetic material with interesting technological applications. In addition, by using the plane-wave expansion method, we studied the photonic band structure of 2D photonic crystals made of ferrofluids with the same nanoparticles. Previous experimental results show that a magnetic field applied perpendicular to the ferrofluid plane agglomerates the magnetic nanoparticles in parallel rods to form a hexagonal 2D photonic crystal. We calculated the photonic band structure of photonic crystals by means of the effective refractive index of the magnetic fluid, basing the study on the Maxwell-Garnett theory, finding that the photonic band structure does not present any band gaps under the action of applied magnetic field strengths used in our experimental conditions.

López, J.; González, Luz E.; Quiñonez, M. F.; Gómez, M. E.; Porras-Montenegro, N.; Zambrano, G.

2014-05-01

237

Hydrodynamic compressibility of high-strength ceramics

In this study we have developed the techniques to investigate the hydrodynamic response of high-strength ceramics by mixing these powders with copper powder, preparing compacts, and performing shock compression tests on these mixtures. Hydrodynamics properties of silicon carbide, titanium diboride, and boron carbide to 30 GPa were examined by this method, and hydrodynamic compression data for these ceramics have been determined. We have concluded, however, that the measurement method is sensitive to sample preparation and uncertainties in shock wave measurements. Application of the experimental technique is difficult and further efforts are needed.

Grady, D.E.

1993-08-01

238

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles from magnetic colloidal suspensions were incorporated in the urethane/urea elastomer (PU/PBDO) by adding to the prepolymers solution in toluene diverse amounts of magnetite grains. It is shown that ferrofluid grains can be efficiently incorporated into the elastomer according to this procedure. Mechanical and optical experiments performed show that the elastomer preparation procedure (casting) introduces a structural anisotropy on the optically isotropic sample. This fact is put in evidence by the measurements of the Young's moduli and orientation of the sample's optical axis under stress. The dependence of the phase shift of both the pure and ferrofluid-doped elastomer samples under strain is linear, and the strain-optic coefficient is show to be linear with the ferrofluid concentration.

Sena, C.; Bailey, C.; Godinho, M. H.; Figueirinhas, J. L.; Palffy-Muhoray, P.; Figueiredo Neto, A. M.

2006-05-01

239

Anisotropy-axis orientation effect on the magnetization of ?-Fe2O3 frozen ferrofluid

NASA Astrophysics Data System (ADS)

The effect of magnetic anisotropy-axis alignment on the superparamagnetic (SPM) and superspin glass (SSG) states in a frozen ferrofluid has been investigated. The ferrofluid studied here consists of maghemite nanoparticles (?-Fe2O3, mean diameter = 8.6 nm) dispersed in glycerine at a volume fraction of ~15%. In the high temperature SPM state, the magnetization of aligned ferrofluid increased by a factor varying between 2 and 4 with respect to that in the randomly oriented state. The negative interaction energy obtained from the Curie-Weiss fit to the high temperature susceptibility in the SPM states as well as the SSG phase onset temperature determined from the linear magnetization curves were found to be rather insensitive to the anisotropy-axis alignment. The low temperature ageing behaviour, explored via 'zero-field cooled magnetization' relaxation measurements, however, shows a distinct difference in the ageing dynamics in the anisotropy-axis aligned and randomly oriented SSG states.

Nakamae, S.; Crauste-Thibierge, C.; Komatsu, K.; L'Hôte, D.; Vincent, E.; Dubois, E.; Dupuis, V.; Perzynski, R.

2010-12-01

240

All-optical modulator based on a ferrofluid core metal cladding waveguide chip

NASA Astrophysics Data System (ADS)

We propose a novel optical intensity modulator based on the combination of a symmetrical metal cladding optical waveguide (SMCW) and ferrofluid, where the ferrofluid is sealed in the waveguide to act as a guiding layer. The light matter interaction in the ferrofluid film leads to the formation of a regular nanoparticle pattern, which changes the phase match condition of the ultrahigh order modes in return. When two lasers are incident on the same spot of the waveguide chip, experiments illustrate all-optical modulation of one laser beam by adjusting the intensity of the other laser. A possible theoretical explanation may be due to the optical trapping and Soret effect since the phenomenon is considerable only when the control laser is effectively coupled into the waveguide.

Han, Qing-Bang; Yin, Cheng; Li, Jian; Tang, Yi-Bin; Shan, Ming-Lei; Cao, Zhuang-Qi

2013-09-01

241

Dielectric response of transformer oil based ferrofluid in low frequency range

NASA Astrophysics Data System (ADS)

In this article, our experimental study of the dynamic dielectric behaviour of transformer oil-based ferrofluid with magnetite nanoparticles is presented. Frequency-dependent dielectric permittivity and dissipation factor were measured within the frequency range from 20 Hz to 2 MHz by a capacitance method. The ferrofluid samples were placed in a liquid crystal cell, and experiments were carried out in an electromagnetically anechoic chamber. Two polarization processes and corresponding relaxations were revealed within the applied frequency range. Schwarz theory of electric double layer polarization is used to explain the low frequency relaxation maximum. Moreover, the shift of the maximum position towards higher frequencies is observed as the magnetic volume fraction in the ferrofluid increases. The related decrease in relaxation time due to higher counterion mobility is analysed. Reduced electric field intensity due to depolarization field, which is dependent on the particle concentration, is proposed as the reason for the maxima shift. This assumption is wholly supported by a complementary experiment.

Rajnak, M.; Kurimsky, J.; Dolnik, B.; Marton, K.; Tomco, L.; Taculescu, A.; Vekas, L.; Kovac, J.; Vavra, I.; Tothova, J.; Kopcansky, P.; Timko, M.

2013-07-01

242

Electromagnetic Vibration Energy Harvester Using Springless Proof Mass and Ferrofluid as a Lubricant

NASA Astrophysics Data System (ADS)

This paper presents an electromagnetic energy harvester using an array of rectangular permanent magnets as springless proof mass and ferrofluid as a lubricating material. Lateral motion of the multi-pole magnet array generates voltage across an array of copper windings formed under the aluminum channel in response to low frequency external vibrations such as human-body-induced motion. A proof-of-concept device has been fabricated and output voltage has been measured at various input frequencies and accelerations provided by a vibration exciter. Device with ferrofluid lubrication generated maximum open-circuit voltage of 0.47V at 3g vibration at 12Hz, which is 8% higher than that of the device without lubricant. Maximum output power of 71.26?W has been obtained at 40.8? with the device with ferrofluid lubrication.

Chae, S. H.; Ju, S.; Choi, Y.; Jun, S.; Park, S. M.; Lee, S.; Lee, H. W.; Ji, C.-H.

2013-12-01

243

Integration of quantum hydrodynamical equation

NASA Astrophysics Data System (ADS)

Quantum hydrodynamics equations describing the dynamics of quantum fluid are a subject of this report (QFD).These equations can be used to decide the wide class of problem. But there are the calculated difficulties for the equations, which take place for nonlinear hyperbolic systems. In this connection, It is necessary to impose the additional restrictions which assure the existence and unique of solutions. As test sample, we use the free wave packet and study its behavior at the different initial and boundary conditions. The calculations of wave packet propagation cause in numerical algorithm the division. In numerical algorithm at the calculations of wave packet propagation, there arises the problem of division by zero. To overcome this problem we have to sew together discrete numerical and analytical continuous solutions on the boundary. We demonstrate here for the free wave packet that the numerical solution corresponds to the analytical solution.

Ulyanova, Vera G.; Sanin, Andrey L.

2007-04-01

244

Meniscus of a ferrofluid around a vertical cylindrical wire carrying electric current

NASA Astrophysics Data System (ADS)

We study the meniscus profiles of ferrofluids in the magnetic field of a vertical current-carrying wire. Measurements of the free ferrofluid surface profile are quantitatively compared with numerical calculations. The theoretical model leads to a second-order ordinary differential equation. All material parameters are determined in independent experiments, therefore no fitting parameters are involved in the calculations. The experimental results can be modeled by the equilibrium of magnetic, gravitational, and interface tension forces. The classical model that neglects interface tension yields significant deviations from the experimental profiles in the parameter range studied.

John, Thomas; May, Kathrin; Stannarius, Ralf

2011-05-01

245

NASA Astrophysics Data System (ADS)

The influence of polydispersity on the magnetization of ferrofluids is studied based on a previously published magnetization equation of state (Szalai and Dietrich, 2011 J. Phys.: Condens. Matter 23 326004) and computer simulations. The polydispersity of the particle diameter is described by the gamma distribution function. Canonical ensemble Monte Carlo simulations have been performed in order to test these theoretical results for the initial susceptibility and the magnetization. The results for the magnetic properties of the polydisperse systems turn out to be in quantitative agreement with our present simulation data. In addition, we find good agreement between our theory and experimental data for magnetite-based ferrofluids.

Szalai, I.; Nagy, S.; Dietrich, S.

2013-11-01

246

Meniscus of a ferrofluid around a vertical cylindrical wire carrying electric current.

We study the meniscus profiles of ferrofluids in the magnetic field of a vertical current-carrying wire. Measurements of the free ferrofluid surface profile are quantitatively compared with numerical calculations. The theoretical model leads to a second-order ordinary differential equation. All material parameters are determined in independent experiments, therefore no fitting parameters are involved in the calculations. The experimental results can be modeled by the equilibrium of magnetic, gravitational, and interface tension forces. The classical model that neglects interface tension yields significant deviations from the experimental profiles in the parameter range studied. PMID:21728648

John, Thomas; May, Kathrin; Stannarius, Ralf

2011-05-01

247

Flow in isothermal layers of ferrofluid by action of uniform rotating magnetic field

The author attempts to determine how intense the flow of a ferrofluid in a rotating magnetic field can become owing to the temperature dependence of the properties when a nonuniform temperature field has been produced within the volume of such a fluid. It was found that in a channel with a strong temperature dependence of viscosity, a uniform rotating magnetic field is capable of effectively influencing the flow of a ferrofluid within nonisothermal layers, which may be of interest in solving problems of heat transfer.

Kashevskii, B.E.

1986-01-01

248

Fabrication of two-dimensional ferrofluid microdroplet lattices in a microfluidic channel

NASA Astrophysics Data System (ADS)

In this paper, we investigated the influences of magnetic field on the ferrofluid droplet generation and the arrangement of the collected droplets in a T-junction microfluidic. Our study includes the field-dependent droplet generation rate, droplet size, as well as the spatial density of the self-assembled droplet collections that were analyzed under the conditions of constant fluid flow rates and capillary number, and all of the field-dependent properties were found inversely proportional to the applied magnetic field strength. In addition, the droplet merging was also able to be avoided by the induced repulsive magnetic force between ferrofluid droplets.

Lee, Chiun-Peng; Lan, Ting-Sheng; Lai, Mei-Feng

2014-05-01

249

Mössbauer evidence of 57Fe3O4 based ferrofluid biodegradation in the brain

NASA Astrophysics Data System (ADS)

The ferrofluid, based on 57Fe isotope enriched Fe3O4 nanoparticles, was synthesized, investigated by Mössbauer spectroscopy method and injected transcranially in the ventricle of the rat brain. The comparison of the Mössbauer spectra of the initial ferrofluid and the rat brain measured in two hours and one week after the transcranial injection allows us to state that the synthesized magnetic 57Fe3O4 nanoparticles undergo intensive biodegradation in live brain and, therefore, they can be regarded as a promising target for a new method of radionuclide-free Mössbauer brachytherapy.

Polikarpov, D.; Cherepanov, V.; Chuev, M.; Gabbasov, R.; Mischenko, I.; Nikitin, M.; Vereshagin, Y.; Yurenia, A.; Panchenko, V.

2014-04-01

250

Magnetic-field-induced structural transitions in a ferrofluid emulsion.

A ferrofluid emulsion, subjected to a slowly increasing magnetic field, exhibits a complicated structural behavior: a gas of Brownian particles changes to columnar solid structures due to induced dipole interaction. Two transition (intermediate) structural regimes are observed: (i) randomly distributed chains and particles and (ii) distinct thin columns and randomly distributed chains and particles. Three structural transition magnetic fields are found, one marking each structural transition, from the initial to the final structural regime. A structural diagram of the structural transition magnetic fields, H(C), versus particle volume fractions, straight phi, is constructed experimentally. Theoretical models of scaling calculations, based upon the dominant magnetic interaction in each structural regime, give the three structural transition magnetic-field relations as H(C1) proportional to straight phi(-1/2), H(C2) proportional to straight phi(-1/4), and H(C3) proportional to (straight phi(gamma)/G2)exp(piG/straight phi((gamma/2))), where gamma=0.39 and G=0.29 for our sample. The final end shape of columns and the relative position between columns show that the end-end repulsion between chains is important in the structural formation. PMID:11304256

Ivey, M; Liu, J; Zhu, Y; Cutillas, S

2001-01-01

251

Magnetoviscosity and thread-like agglomerations in ferrofluids

NASA Astrophysics Data System (ADS)

We report on experiments and simulations performed on small non-magnetic glass balls falling under gravity through a magnetized ferrofluid. The applied magnetic field is oriented horizontally, normal to the fall, and is uniform but its magnitude can be adjusted over a wide range. Using the Advanced Photon Source x-ray beamline at Argonne, we were able to achieve sufficient spatial and temporal resolution to track the dynamics of these 500 ?m diameter spheres simultaneously with an array of magnetic particle macro-chains -- thread-like agglomerations each several mm long and 2-10 ?m thick. The enhanced drag induced by the macro-chains is enormous: up to four times larger than for unmagnetized fluid, a value greater than is predicted by the prevailing magneto-viscosity model. We provide direct visualization of a possible mechanism by which macro-chains impede the transverse motion of spheres. Numerical simulations can reproduce the observed drag, without modeling it physically, by implementing a simple magnetization dependent anisotropic viscosity.

Yecko, Philip; Cali, A.; Lee, W.-K.; Nunez, S.; Prescod, J.; Smith, R.; Trubatch, A. D.; Vieira, M.

2011-11-01

252

Ferrofluids are stable colloidal suspensions of magnetic particles in various carrier liquids with high saturation magnetizations, which can be manipulated in virtually any fashion, defying gravitational or viscous forces in response to external magnetic fields. In this report, the authors review the results of their investigation of the potential of ferrofluids (1) to accurately and effectively guide reactants (for in-situ treatment) or barrier liquids (low-viscosity permeation grouts) to contaminated target zones in the subsurface using electromagnetic forces, and (2) to trace the movement and position of liquids injected in the subsurface using geophysical methods. They investigate the use of ferrofluids to enhance the efficiency of in-situ treatment and waste containment through (a) accurate guidance and delivery of reagent liquids to the desired subsurface contamination targets and/or (b) effective sweeping of the contaminated zone as ferrofluids move from the application point to an attracting magnet/collection point. They also investigate exploiting the strong magnetic signature of ferrofluids to develop a method for monitoring of liquid movement and position during injection using electromagnetic methods. The authors demonstrated the ability to induce ferrofluid movement in response to a magnetic field, and measured the corresponding magnetopressure. They demonstrated the feasibility of using conventional magnetometry for detecting subsurface zones of various shapes containing ferrofluids for tracing liquids injected for remediation or barrier formation. Experiments involving spherical, cylindrical and horizontal slabs showed a very good agreement between predictions and measurements.

Moridis, G.J.; Borglin, S.E.; Oldenburg, C.M.; Becker, A.

1998-03-01

253

Results of experiments on small-angle neutron scattering from ferrofluids on polar carriers (pentanol, water, methyl-ethyl-ketone), with double-layer sterical stabilization of magnetic nanoparticles, are reported. Several types of spatial structural organization are observed. The structure of highly stable pentanol-based samples is similar to that of stable ferrofluids based on organic non-polar carriers (e.g., benzene) with mono-layer covered magnetic nanoparticles. At the same time, the effect of the interparticle interaction on the scattering is stronger in polar ferrofluids because of the structural difference in the surfactant shell. The structure of the studied methyl-ethyl-ketone- and water-based ferrofluids essentially different from the previous case. The formation of large (>100 nm in size) elongated or fractal aggregates, respectively, is detected even in the absence of external magnetic field, which corresponds to weaker stability of these types of ferrofluids. The structure of the fractal aggregates in water-based ferrofluids does not depend on the particle concentration, but it is sensitive to temperature. A temperature increase results in a decrease in their fractal dimension reflecting destruction of the aggregates. In addition, in water-based ferrofluids these aggregates consist of small (radius approximately 10 nm) and temperature-stable primary aggregates. PMID:16102775

Avdeev, M V; Aksenov, V L; Balasoiu, M; Garamus, V M; Schreyer, A; Török, Gy; Rosta, L; Bica, D; Vékás, L

2006-03-01

254

Hydrodynamic Simulations of Planetary Rings

NASA Astrophysics Data System (ADS)

Simulations of rings have traditionally been done using N-body methods, granting insight into the interactions of individual ring particles on varying scales. However, due to the scale of a typical ring system and the sheer number of particles involved, a global N-body simulation is too computationally expensive, unless particle collisions are replaced by stochastic forces (Bromley & Kenyon, 2013). Rings are extraordinarily flat systems and therefore are well-suited to existing geophysical shallow-water hydrodynamics models with well-established non-linear advection methods. By adopting a general relationship between pressure and surface density such as a polytropic equation of state, we can modify the shallow-water formula to treat a thin, compressible, self-gravitating, shearing fluid. Previous hydrodynamic simulations of planetary rings have been restricted to axisymmetric flows and therefore have not treated the response to nonaxisymmetric perturbations by moons (Schmidt & Tscharnuter 1999, Latter & Ogilvie 2010). We seek to expand on existing hydrodynamic methods and, by comparing our work with complementary N-body simulations and Cassini observations, confirm the veracity of our results at small scales before eventually moving to a global domain size. We will use non-Newtonian, dynamically variable viscosity to model the viscous transport caused by unresolved self-gravity wakes. Self-gravity will be added to model the dynamics of large-scale structures, such as density waves and edge waves. Support from NASA Outer Planets and Planetary Geology and Geophysics programs is gratefully acknowledged.

Miller, Jacob; Stewart, G. R.; Esposito, L. W.

2013-10-01

255

NSDL National Science Digital Library

The following websites are useful tools in understanding how energy is transferred from place to place through waves. Start by downloading the assignment and then begin with website number 1 and continue until you have visited all three websites. Begin by downloading the IA Waves Internet Assignment: IA Waves Internet Assignment You will answer the questions in Microsoft Word and then e-mail the assignment to me. Website #1: Read about basic information on waves and answer the questions from part 1 of the IA Waves Guide: Basic Wave Information Website #2: Follow the instructions for the following ...

Hansen, Mr.

2010-11-12

256

Algorithm refinement for fluctuating hydrodynamics

This paper introduces an adaptive mesh and algorithmrefinement method for fluctuating hydrodynamics. This particle-continuumhybrid simulates the dynamics of a compressible fluid with thermalfluctuations. The particle algorithm is direct simulation Monte Carlo(DSMC), a molecular-level scheme based on the Boltzmann equation. Thecontinuum algorithm is based on the Landau-Lifshitz Navier-Stokes (LLNS)equations, which incorporate thermal fluctuations into macroscopichydrodynamics by using stochastic fluxes. It uses a recently-developedsolver for LLNS, based on third-order Runge-Kutta. We present numericaltests of systems in and out of equilibrium, including time-dependentsystems, and demonstrate dynamic adaptive refinement by the computationof a moving shock wave. Mean system behavior and second moment statisticsof our simulations match theoretical values and benchmarks well. We findthat particular attention should be paid to the spectrum of the flux atthe interface between the particle and continuum methods, specificallyfor the non-hydrodynamic (kinetic) time scales.

Williams, Sarah A.; Bell, John B.; Garcia, Alejandro L.

2007-07-03

257

Waves in Radial Gravity Using Magnetic Fluid

NASA Technical Reports Server (NTRS)

Terrestrial laboratory experiments studying various fluid dynamical processes are constrained, by being in an Earth laboratory, to have a gravitational body force which is uniform and unidirectional. Therefore fluid free-surfaces are horizontal and flat. Such free surfaces must have a vertical solid boundary to keep the fluid from spreading horizontally along a gravitational potential surface. In atmospheric, oceanic, or stellar fluid flows that have a horizontal scale of about one-tenth the body radius or larger, sphericity is important in the dynamics. Further, fluids in spherical geometry can cover an entire domain without any sidewall effects, i.e. have truly periodic boundary conditions. We describe spherical body-force laboratory experiments using ferrofluid. Ferrofluids are dilute suspensions of magnetic dipoles, for example magnetite particles of order 10 nm diameter, suspended in a carrier fluid. Ferrofluids are subject to an additional body force in the presence of an applied magnetic field gradient. We use this body force to conduct laboratory experiments in spherical geometry. The present study is a laboratory technique improvement. The apparatus is cylindrically axisymmetric. A cylindrical ceramic magnet is embedded in a smooth, solid, spherical PVC ball. The geopotential field and its gradient, the body force, were made nearly spherical by careful choice of magnet height-to-diameter ratio and magnet size relative to the PVC ball size. Terrestrial gravity is eliminated from the dynamics by immersing the "planet" and its ferrofluid "ocean" in an immiscible silicone oil/freon mixture of the same density. Thus the earth gravity is removed from the dynamics of the ferrofluid/oil interface and the only dynamically active force there is the radial magnetic gravity. The entire apparatus can rotate, and waves are forced on the ferrofluid surface by exterior magnets. The biggest improvement in technique is in the wave visualization. Fluorescing dye is added to the oil/freon mixture and an argon ion laser generates a horizontal light that can be scanned vertically. Viewed from above, the experiment is a black circle with wave deformations surrounded by a light background. A contour of the image intensity at any light sheet position gives the surface of the ferrofluid "ocean" at that "latitude". Radial displacements of the waves as a function of longitude are obtained by subtracting the contour line positions from a no-motion contour at that laser sheet latitude. The experiments are run by traversing the forcing magnet with the laser sheet height fixed and images are frame grabbed to obtain a time-series at one latitude. The experiment is then re-run with another laser-sheet height to generate a full picture of the three-dimensional wave structure in the upper hemisphere of the ball as a function of time. We concentrate here on results of laboratory studies of waves that are important in Earth's atmosphere and especially the ocean. To get oceanic scaling in the laboratory, the experiment must rotate rapidly (4-second rotation period) so that the wave speed is slow compared to the planetary rotation speed as in the ocean. In the Pacific Ocean, eastward propagating Kelvin waves eventually run into the South American coast. Theory predicts that some of the wave energy should scatter into coastal-trapped Kelvin waves that propagate north and south along the coast. Some of this coastal wave energy might then scatter into mid-latitude Rossby waves that propagate back westward. Satellite observations of the Pacific Ocean sea-surface temperature and height seem to show signatures of westward propagating mid-latitude Rossby waves, 5 to 10 years after the 1982-83 El Nino. The observational data is difficult to interpret unambiguously owing to the large range of motions that fill the ocean at shorter timescales. This series of reflections giving eastward, north- ward, and then westward traveling waves is observed cleanly in the laboratory experiments, confirming the theoretical expectations

Ohlsen, D. R.; Hart, J. E.; Weidman, P. D.

1999-01-01

258

Observations of ferrofluid flow under a uniform rotating magnetic field in a spherical cavity

NASA Astrophysics Data System (ADS)

Flow of a ferrofluid in spherical and cylindrical geometries were measured under the influence of a uniform rotating magnetic field produced by two perpendicular spherical coils, a so-called fluxball, excited by quadrature currents. Using an ultrasound velocity profile technique and a commercial oil based ferrofluid (EFH1, Ferrotec) we observed rotational flow around the z-axis. In comparison, the radial component of the flow was found to be negligible. Results show that the magnitude of the azimuthal velocity profile increases as the applied magnetic field amplitude increases. This behavior is also observed for ferrofluid in a cylindrical container placed inside the fluxball cavity and inside a two-pole stator winding. These results indicate that inhomogeneities in the magnetic field produced by slots and finite height of the stator winding used in prior experiments are not the source of previously observed flows produced by a two pole stator winding. The experiments reported here either point to the existence of non-uniform demagnetizing magnetic fields due to the finite height of the cylindrical container, the existence of couple stresses and spin viscosity in ferrofluids, or to the need to develop alternate governing and constitutive equations capable of describing the experimental observations.

Torres-Díaz, Isaac; Rinaldi, Carlos; Khushrushahi, Shahriar; Zahn, Markus

2012-04-01

259

Specific bilayer on the surface of water-based ferrofluids: Structure and particular persistence

NASA Astrophysics Data System (ADS)

The structure of sterically stabilized water-based ferrofluid in the vicinity of free interface with a gaseous atmosphere is studied by means of X-ray reflectometry and grazing incidence X-ray diffraction. Experimental data unambiguously show that in-depth distribution of the magnetic nano-particles and surfactant molecules in the ferrofluid layer close to the interface is essentially non-uniform. Particularly, bulk homogeneous liquid is covered with a relatively thick layer (about 200 A?) with enhanced concentration of the surfactant and reduced concentration of the magnetic particles, which is consequently overlayed with a thin layer (about 40 A?) with increased concentration of the particles. Having the aim to obtain more homogeneous and controllable ferrofluid surface, we tried to eliminate this specific bilayer in two different ways--mechanically and by means of long-term sedimentation of a sample in a dropping funnel under hexadecane. However, in both case the same surface structure but with slightly different parameters have been observed. Apparently, the described bilayer can be assumed as an essential equilibrium feature inevitably existing at the interface of water-based ferrofluids with gas.

Vorobiev, A.; Konovalov, O.; Khassanov, A.; Orlova, D.; Gordeev, G.

2011-11-01

260

Stationary off-equilibrium magnetization in ferrofluids under rotational and elongational Flow.

The magnetization of a ferrofluid, which is exposed to a flow, was recently proposed to depend on the symmetric velocity gradients (elongational flow). This is demonstrated by an experimental setup, which allows one to evaluate the transport coefficient associated with the elongational flow contribution. PMID:12144415

Odenbach, Stefan; Müller, Hanns Walter

2002-07-15

261

Nonmonotonic field-dependent magnetic permeability of a paramagnetic ferrofluid emulsion.

The ferrofluid emulsion, made of kerosene-based ferrofluid droplets suspended in nonmiscible aviation oil, demonstrates experimentally the nonmonotonic dependence of the effective magnetic permeability as a function of the uniform static magnetic field. In weak fields the emulsion permeability rapidly grows; it reaches its maximum at fields on the order of 1 kA/m; after that, it decays to zero. The theoretical explanation of the effect, as we show here, could be based on the following idea: In a weak magnetic field the growth of the induced droplet magnetic moment is faster than the linear one due to the droplet elongation accompanied by the reduction of the demagnetizing field. Further increase of the external magnetic field strength cannot lead to a significant decrease of the demagnetizing field, as the droplets are already highly elongated. On the other hand, the magnetic susceptibility of the ferrofluid reduces with the field strength. Thus, the effective magnetic permeability of the ferrofluid suspension starts decreasing. The developed theoretical model describes well the experimental observations. PMID:22680473

Ivanov, Alexey O; Kuznetsova, Olga B

2012-04-01

262

A novel biomimetic material--glycine-PVA ferrofluid that crosses the blood-brain barrier.

The present study describes the efficacy of the glycine-poly(vinyl)alcohol ferrofluid as a contrast enhancer for Magnetic resonance imaging. Interaction between inorganic minerals and biomolecules are extremely unique and interesting. The results demonstrate that ferro fluids can be a good contrast enhancer for Magnetic Resonance Imaging as seen in the very first results after MRI studies. PMID:21485812

Nayar, Suprabha; Guha, Avijit

2011-02-01

263

HULL (Hydrodynamics Unlimited) Hydrodynamics Computer Code.

National Technical Information Service (NTIS)

The HULL (Hydrodynamics Unlimited) code is a family of hydrocodes at the Air Force Weapons Laboratory. Within the code are contained two and three-dimensional Eulerian difference schemes which are first and second order accurate. Many computational aids s...

M. A. Fry R. E. Durrett G. P. Ganong D. A. Matuska M. D. Stucker

1976-01-01

264

Three-dimensional hydrodynamic hot-spot

The basic processes in the shock initiation of heterogeneous explosives have been investigated theoretically using a model of a cube of nitromethane containing 91 cubic air holes. The interaction of a shock wave with a single air hole and a matrix of air holes in PETN, HMX, and TATB has been numerically modeled. The interaction of a shock wave with the density discontinuities, the resulting hot-spot formation and interaction, and the buildup to propagating detonation were computed using three-dimensional numerical Eulerian hydrodynamics with Arrhenius chemical reaction and accurate equations of state according to the hydrodynamic hot-spot model. The basic processes in the desensitization of a heterogeneous explosive by preshocking with a shock pressure too low to cause propagating detonation was numerically modeled. The basic differences between shock sensitive explosives such as PETN or HMX and shock insensitive explosives such as TATB or NQ may be described using the hydrodynamic hot-spot model.

Mader, C.L.

1984-01-01

265

Hydrodynamic Characteristics of Pile-Supported Vertical Wall Breakwaters

This paper describes the hydrodynamic characteristics of a pile-supported vertical wall breakwater, the upper part of which is a vertical wall, and the lower part consisting of an array of vertical piles. For regular waves, using the eigenfunction expansion method, a numerical model has been developed that can compute wave transmission, reflection, and run-up, and wave force acting on the

Kyung-Duck Suh; Sungwon Shin

2006-01-01

266

National Technical Information Service (NTIS)

Ferrofluids are stable colloidal suspensions of magnetic particles in various carrier liquids with high saturation magnetizations, which can be manipulated in virtually any fashion, defying gravitational or viscous forces in response to external magnetic ...

G. J. Moridis S. E. Borglin C. M. Oldenburg A. Becker

1998-01-01

267

Ergoregion instability: The hydrodynamic vortex

NASA Astrophysics Data System (ADS)

Four-dimensional, asymptotically flat spacetimes with an ergoregion but no horizon have been shown to be linearly unstable against a superradiant-triggered mechanism. This result has wide implications in the search for astrophysically viable alternatives to black holes, but also in the understanding of black holes and Hawking evaporation. Here we investigate this instability in detail for a particular setup that can be realized in the laboratory: the hydrodynamic vortex, an effective geometry for sound waves, with ergoregion and without an event horizon.

Oliveira, Leandro A.; Cardoso, Vitor; Crispino, Luís C. B.

2014-06-01

268

This paper demonstrates the use of magnetically controlled microfluidic devices to produce monodispersed ferrofluid emulsions. By applying a uniform magnetic field on flow-focusing and T-junction configurations, the size of the ferrofluid emulsions can be actively controlled. The influences of the flow rates, the orientation, and the polarity of the magnetic field on the size of ferrofluid emulsions produced in both flow-focusing and T-junction configurations are compared and discussed. PMID:22060502

Tan, Say Hwa; Nguyen, Nam-Trung

2011-09-01

269

Macrostatistics and Fluctuating Hydrodynamics

NASA Astrophysics Data System (ADS)

We extend our earlier macrostatistical treatment of hydrodynamical fluctuations about nonequilibrium steady states to viscous fluids. Since the scale dependence of the Navier-Stokes equations precludes the applicability of any infinite scale (hydrodynamical) limit, this has to based on the generic model of a large but finite system, rather than an infinite one. On this basis, together with the assumption of Onsager's regression hypothesis and conditions of local equilibrium and chaoticity, we show that the hydrodynamical fluctuations of a reservoir driven fluid about a nonequilibrium steady state execute a Gaussian Markov process that constitutes a mathematical structure for a generalised version of Landau's fluctuating hydrodynamics and generically carries long range spatial correlations.

Sewell, Geoffrey L.

2012-10-01

270

Raman study of magnetic field effects on surfacted and ionic ferrofluids

NASA Astrophysics Data System (ADS)

We report Raman spectroscopic measurements on surfacted (SFF) and ionic ferrofluids in magnetic fields up to 0.25 T. For the SFF Raman spectra display the characteristic broad bands associated with vibrations of surfactant and water molecules. With increasing magnetic field the overall Raman intensity decreases abruptly up to about 50 mT, leveling out above this field. In contrast, at high magnetic fields a broad peak which is attributed to a magnetic excitation becomes apparent in the spectra at frequencies in the range of 4000 cm-1. Our results can be explained in terms of a local increase in magnetic-particle concentration and the formation of ordered structures in the presence of a magnetic field. The Raman spectra of the electrostatically stabilized ferrofluids, which are dominated by the H 2O stretching vibrations, exhibit a different magnetic-field behavior of their intensity probably indicating the incipient formation of large nanograin clusters.

Weber, J. E.; Goñi, A. R.; Thomsen, C.

2004-06-01

271

Magnetic characterization by SQUID and FMR of a biocompatible ferrofluid based on Fe3O4

NASA Astrophysics Data System (ADS)

Biocompatible superparamagnetic iron oxide nanoparticles of magnetite coated with dextran were magnetically characterized using the techniques of SQUID (superconducting quantum interference device) magnetometry and ferromagnetic resonance (FMR). The SQUID magnetometry characterization was performed by isothermal measurements under applied magnetic field using the methods of zero-field-cooling (ZFC) and field-cooling (FC). The magnetic behavior of the nanoparticles indicated their superparamagnetic nature and it was assumed that they consisted exclusively of monodomains. The transition to a blocked state was observed at the temperature TB = (43 ± 1) K for frozen ferrofluid and at (52 ± 1) K for the lyophilized ferrofluid samples. The FMR analysis showed that the derivative peak-to-peak linewidth (?HPP), gyromagnetic factor (g), number of spins (NS), and spin-spin relaxation time (T2) were strongly dependent on both temperature and super-exchange interaction. This information is important for possible nanotechnological applications, mainly those which are strongly dependent on the magnetic parameters.

Gamarra, L. F.; Pontuschka, W. M.; Mamani, J. B.; Cornejo, D. R.; Oliveira, T. R.; Vieira, E. D.; Costa-Filho, A. J.; Amaro, E., Jr.

2009-03-01

272

Thermal conductivity measurements on ferrofluids with special reference to measuring arrangement

NASA Astrophysics Data System (ADS)

Material properties like viscosity and sound propagation in colloidal suspensions of magnetic nanoparticles, so-called ferrofluids, are known to depend on external magnetic fields due to structure formation of the magnetic particles. In this experimental study we investigate the effect of magnetically driven structure formation on heat flux in ferrofluids on the basis of thermal conductivity measurements in variation of an external magnetic field. Therefore an improved measuring device based on the plane heat source instead of the standard hot wire method is used to enable both parallel and perpendicular orientation of magnetic field and heat flux. Thermal conductivity measurements are carried out in variation of strength and direction of an external magnetic field relative to heat flux. Unlike former experimental investigations for the first time the results show qualitative consistency with theoretical predictions for both orientations.

Krichler, M.; Odenbach, S.

2013-01-01

273

The magnetic assembly of polymer colloids in a ferrofluid and its display applications.

Nonmagnetic polymer colloids have been assembled into colloidal photonic crystals in a ferrofluid by applying an external magnetic field based on the dipole-dipole interactions of "magnetic holes". The photonic crystal disassembles immediately when the magnetic field is removed. The mechanism of assembly can be explained by two simultaneous processes: phase separation and colloidal assembly. In this work, increasing the size of the building blocks still produces colorful photonic crystals due to their 2nd order diffraction. With a larger building block, the magnetic response between the polymer colloids is greatly enhanced so that an instant and reversible assembly/disassembly can be realized in a much weaker magnetic field and lower ferrofluid concentration. Based on these investigations, a magnetically controlled photonic display unit has been fabricated, which works in a weak magnetic field, has stable reflection signals and possesses fast and reversible on/off switching of reflections. PMID:22297654

Liu, Jing; Mao, Yiwu; Ge, Jianping

2012-03-01

274

Phase transitions in a ferrofluid at magnetic-field-induced microphase separation.

In the presence of a magnetic field applied perpendicular to a thin sample layer, a suspension of magnetic colloidal particles (ferrofluid) can form spatially modulated phases with a characteristic length determined by the competition between dipolar forces and short-range forces opposing density variations. We introduce models for thin-film ferrofluids in which magnetization and particle density are viewed as independent variables and in which the nonmagnetic properties of the colloidal particles are described either by a lattice-gas entropy or by the Carnahan-Starling free energy. Our description is particularly well suited to the low-particle-density regions studied in many experiments. Within mean-field theory, we find isotropic, hexagonal and stripe phases, separated in general by first-order phase boundaries. PMID:11690032

Lacoste, D; Lubensky, T C

2001-10-01

275

Magnetic-field tunable transmittance in a ferrofluid-filled silicon nitride photonic crystal slab

NASA Astrophysics Data System (ADS)

A numerical simulation was performed to demonstrate the active manipulation of the transmittance spectra in a ferrofluid-filled silicon nitride (SiN) photonic crystal slab (PCS) with magnetic field applied perpendicularly to the plane. Many sharp transmittance resonances were found to be correlated with the modes extracted from band structure calculations, where they show red-shift and mutual approach as the external magnetic field increases. By changing the angle of the incident light, we found strong coupling modes because of their asymmetric electric field distributions. This in situ control of transmittance properties of ferrofluid-filled SiN PCS should open up new applications for designing filters, mirrors and displacement sensors in compact optical devices.

Lee, H. M.; Horng, L.; Wu, J. C.

2011-02-01

276

Ferrofluid aggregation in chains under the influence of a magnetic field.

The theory of particle association in flexible chains in dilute ferrofluids is generalized to the case of an arbitrarily strengthened magnetic field. The chain distribution in dynamic equilibrium is obtained on the basis of free energy minimization method under the neglect of interchain interaction. The chain partition function is calculated analytically with the help of the rotation matrix technique under the condition when the interparticle dipole-dipole interaction between the nearest neighboring ferroparticles in each chain is taken into account. At weak fields, the chain distribution and the initial susceptibility are shown to be dependent on the value of the correlation coefficient describing the zero field mutual orientational correlations between the magnetic moments of two neighboring ferroparticles in a chain. The internal chain orientational correlations and the field dependent chain lengthening result in higher magnetization of the aggregated ferrofluid in comparison with the Langevin magnetization. PMID:15600619

Mendelev, Valentin S; Ivanov, Alexey O

2004-11-01

277

NASA Astrophysics Data System (ADS)

Separate determination of the nuclear and magnetic contributions to the scattering intensity by means of a contrast variation method applied in a small angle neutron scattering experiment of nonpolarized neutrons in ferrofluids in early 90 's at the MURN instrument is reviewed. The nuclear scattering contribution gives the features of the colloidal particle dimensions, surfactant shell structure and the solvent degree penetration to the macromolecular layer. The magnetic scattering part is compatible to the models where is supposed that the particle surface has a nonmagnetic layer. Details on experimental "Grabcev method" in obtaining separate nuclear and magnetic contributions to the small angle neutron scattering intensity of unpolarized neutrons are emphasized for the case of a high quality ultrastabile benzene-based ferrofluid with magnetite nanoparticles.

Balasoiu, Maria; Kuklin, Alexander

2012-03-01

278

Synthesis and characterization of size-controlled cobalt-ferrite-based ionic ferrofluids

NASA Astrophysics Data System (ADS)

Size-controlled synthesis of cobalt-ferrite nanoparticles, their passivation and peptization as stable ferrofluids are reported. Transmission electron microscopy and Mössbauer spectroscopy were used as characterization techniques. Particles with little change in size distribution, in the 10-15 nm diameter ranges, were obtained using stirring speeds between 2700 and 8100 rpm. The anomalous diffusion has been used to explain the nanoparticle size-control mechanism.

Morais, P. C.; Garg, V. K.; Oliveira, A. C.; Silva, L. P.; Azevedo, R. B.; Silva, A. M. L.; Lima, E. C. D.

2001-01-01

279

Overcoming the Diffusion Barrier: Ultra-Fast MicroScale Mixing Via Ferrofluids

We report on the design, development, fabrication and characterization of a novel, micro-scale mixing device based on stable water suspensions of magnetic nanoparticles (i.e. ferrofluids). The micromixer prototypes are built using standard microfabrication and simple soft-lithography, and the design can be incorporated as a sub-system into any chemical micro-reactor or a miniaturized biological sensor. The devices achieve mixing virtually instantaneously

Leidong Mao; Hur Koser

2007-01-01

280

Synthesis and characterization of size-controlled cobalt-ferrite-based ionic ferrofluids

Size-controlled synthesis of cobalt-ferrite nanoparticles, their passivation and peptization as stable ferrofluids are reported. Transmission electron microscopy and Mössbauer spectroscopy were used as characterization techniques. Particles with little change in size distribution, in the 10–15nm diameter ranges, were obtained using stirring speeds between 2700 and 8100rpm. The anomalous diffusion has been used to explain the nanoparticle size-control mechanism.

P. C. Morais; V. K. Garg; A. C. Oliveira; L. P. Silva; R. B. Azevedo; A. M. L. Silva; E. C. D. Lima

2001-01-01

281

Continuous separation of non-magnetic particles through negative magnetophoresis inside ferrofluids

We present a simple, low-cost, effective, and label-free continuous flow non-magnetic microparticle separation scheme in a microfluidic device under static magnetic fields. The separation process is based on negative magnetophoresis and uses water-based ferrofluids. We exploit the difference in particle sizes to achieve continuous binary separation of fluorescent microparticles with high throughput and efficiency. We demonstrate size-based separation (2.1 ?m

Taotao Zhu; Francisco Marrero; Leidong Mao

2010-01-01

282

The purpose of this study was to compare the effects of magnetic thermal ablation in different porcine tissues using either\\u000a a singular injection or a continuous infusion of superparamagnetic iron oxide nanoparticles. In the first setting samples\\u000a of three ferrofluids containing different amounts of iron (1:171, 2:192, and 3:214 mg\\/ml) were singularly interstitially injected\\u000a into specimens of porcine liver, kidney,

Philipp Bruners; Michael Hodenius; Martin Baumann; Jessica Oversohl; Rolf W. Günther; Thomas Schmitz-Rode; Andreas H. Mahnken

2008-01-01

283

Entrainment by a rotating magnetic field of a ferrofluid contained in a sphere.

Entrainment of a ferrofluid contained in a sphere by a rotating uniform magnetic field is studied on the basis of spin-diffusion theory. The equations for flow velocity and spin velocity, coupled to Maxwell's equations of magnetostatics, are solved analytically to second order in the applied magnetic field. A similar derivation holds in electrohydrodynamics for a polar liquid contained in a sphere and subject to a rotating electrical field. PMID:22181267

Felderhof, B U

2011-10-01

284

The aim of this work has been the investigation of the anisotropy of the viscosity of a ferrofluid with magnetically interacting particles which are able to form structures in an applied magnetic field. The results of the experiments show a significant deviation from the case of a fluid without strong dipolar interactions. Furthermore, we have determined the dependence of the ratio of the viscosity coefficients on shear rate providing an insight into the microstructural reasons for the observed effects. PMID:21841240

Gerth-Noritzsch, M; Yu Borin, D; Odenbach, S

2011-08-12

285

Ferrofluidity in a Two-Component Dipolar Bose-Einstein Condensate

It is shown that the interface in a two-component Bose-Einstein condensate (BEC) with a dipole-dipole interaction spontaneously develops patterns similar to those formed in a ferrofluid. Hexagonal, labyrinthine, solitonlike structures, and hysteretic behavior are numerically demonstrated. Superflow is found to circulate around the hexagonal pattern at rest, offering evidence of supersolidity. The system sustains persistent current with a vortex line pinned by the hexagonal pattern. These phenomena may be realized using a {sup 52}Cr BEC.

Saito, Hiroki [Department of Applied Physics and Chemistry, University of Electro-Communications, Tokyo 182-8585 (Japan); Kawaguchi, Yuki [Department of Physics, University of Tokyo, Tokyo 113-0033 (Japan); Ueda, Masahito [Department of Physics, University of Tokyo, Tokyo 113-0033 (Japan); ERATO Macroscopic Quantum Project, JST, Tokyo 113-8656 (Japan)

2009-06-12

286

Dipolar Interactions between Iron-Oxide Nanoparticles in Frozen Ferrofluids and Ferronematics

We present a detailed study of the magnetic behavior of iron-oxide (gamma-Fe2O3 and Fe3O4) nanoparticles constituents of ferrofluids (FF's) with average particle sizes = 2.5 and 10 nm. The particles were dispersed in the frozen liquid carrier (pure FF) and in a frozen lyotropic liquid crystalline matrix in the nematic phase or ferronematic (FN) (ferrolyomesophase). Both FF and FN phases

G. F. Goya; S. L. Gómez; S. M. Shibli

2011-01-01

287

NASA Astrophysics Data System (ADS)

The difference between success or failure of chemotherapy depends not only on the drug itself but also on how it is delivered to its target. Biocompatible ferrofluids (FF) are paramagnetic nanoparticles, that may be used as a delivery system for anticancer agents in locoregional tumor therapy, called "magnetic drug targeting". Bound to medical drugs, such magnetic nanoparticles can be enriched in a desired body compartment (tumor) using an external magnetic field, which is focused on the area of the tumor. Through this form of target directed drug application, one attempts to concentrate a pharmacological agent at its site of action in order to minimize unwanted side effects in the organism and to increase its locoregional effectiveness. Tumor bearing rabbits (VX2 squamous cell carcinoma) in the area of the hind limb, were treated by a single intra-arterial injection (A. femoralis) of mitoxantrone bound ferrofluids (FF-MTX), while focusing an external magnetic field (1.7 Tesla) onto the tumor for 60 minutes. Complete tumor remissions could be achieved in these animals in a dose related manner (20% and 50% of the systemic dose of mitoxantrone), without any negative side effects, like e.g. leucocytopenia, alopecia or gastrointestinal disorders. The strong and specific therapeutic efficacy in tumor treatment with mitoxantrone bound ferrofluids may indicate that this system could be used as a delivery system for anticancer agents, like radionuclids, cancer-specific antibodies, anti-angiogenetic factors, genes etc.

Alexiou, Ch.; Schmid, R.; Jurgons, R.; et al.

288

Variations in optical transmittance with magnetic fields in nanosized FePt ferrofluid

NASA Astrophysics Data System (ADS)

The optical transmittance increases with decreasing the concentration of FePt in both water-based and hexane-based ferrofluids. However, under an applied magnetic field H, the transmittance T increases with increasing H field. The variation in transmittance ?T increases rapidly for samples in hexane at H=182 Oe. However, ?T is very small for samples in distilled water. This can be explained due to the different aggregation ability of magnetic particles in ferrofluid. For the samples in hexane, its larger aggregation ability makes the magnetic particles easier to agglomerate and becomes much more chainlike elongated along the perpendicular magnetic field. Thus, it makes the area covered by the droplets per unit area in ferrofluid decrease and the ?T increases with increasing the magnetic field. However, for samples in hexane, the optical properties may also be related with the Mie resonance. At H>60 Oe, the particle aggregation occurs and elongates more along the magnetic fields. This would cause the longitudinal plasmon resonance absorption to shift to a longer wavelength. Therefore, the absorption increases and the variation in transmittance ?T decreases with increasing the incident wavelength.

Wu, Kung-Tung; Yao, Y. D.; Chang, Cheng-Wei

2009-04-01

289

Direct observation of dipolar chains in iron ferrofluids by cryogenic electron microscopy.

A key issue in research on ferrofluids (dispersions of magnetic colloids) is the effect of dipolar interactions on their structure and phase behaviour, which is not only important for practical applications but gives fundamental insight in dipolar fluids in general. In 1970, de Gennes and Pincus predicted a Van der Waals-like phase diagram and the presence of linear chains of particles in ferrofluids in zero magnetic field. Despite many experimental studies, no direct evidence of the existence of linear chains of dipoles has been reported in the absence of magnetic field, although simulations clearly show the presence of chain-like structures. Here, we show in situ linear dipolar structures in ferrofluids in zero field, visualized on the particle level by electron cryo-microscopy on thin, vitrified films of organic dispersions of monodisperse metallic iron particles. On systematically increasing the particle size, we find an abrupt transition from separate particles to randomly oriented linear aggregates and branched chains or networks. When vitrified in a permanent magnetic field, these chains align and form thick elongated structures, indicating lateral attraction between parallel dipole chains. These findings show that the experimental model used is well suited to study the structural properties of dipolar particle systems. PMID:12612691

Butter, K; Bomans, P H H; Frederik, P M; Vroege, G J; Philipse, A P

2003-02-01

290

Design of water-based ferrofluids as contrast agents for magnetic resonance imaging.

We report the synthesis, characterization and relaxometric study of ferrofluids based on iron oxide, with potential for use as magnetic resonance imaging (MRI) contrast agents (CAs). The effect of different cost-effective, water-based surface modification approaches which can be easily scaled-up for the large scale synthesis of the ferrofluids has been investigated. Surface modification was achieved by silanization, and/or coating with non-toxic commercial dispersants (a lauric polysorbate and a block copolymer with pigment affinic groups, namely Tween 20 and Disperbyk 190) which were added after or during iron oxide nanoparticle synthesis. It was observed that all the materials synthesized functioned as negative contrast agents at physiological temperature and at frequencies covered by clinical imagers. The relaxometric properties of the magnetic nanoparticles were significantly improved after surface coating with stabilizers compared to the original iron oxide nanoparticles, with particular reference to the silica-coated magnetic nanoparticles. The results indicate that the optimization of the preparation of colloidal magnetic ferrofluids by surface modification is effective in the design of novel contrast agents for MRI by enabling better or more effective interaction between the coated iron oxide nanoparticles and protons present in their aqueous environment. PMID:21345440

Casula, Maria F; Corrias, Anna; Arosio, Paolo; Lascialfari, Alessandro; Sen, Tapas; Floris, Patrizia; Bruce, Ian J

2011-05-01

291

Deformation of ferrofluid marbles in the presence of a permanent magnet.

This paper investigates the deformation of ferrofluid marbles in the presence of a permanent magnet. Ferrofluid marbles are formed using a water-based ferrofluid and 1 ?m hydrophobic polytetrafluoride particles. A marble placed on a Teflon coated glass plate deforms under gravity. In the presence of a permanent magnet, the marble is further deformed with a larger contact area. The geometric parameters are normalized by the radius of an undistorted spherical marble. The paper first discusses a scaling relationship between the dimensionless radius of the contact area as well as the dimensionless height and the magnetic Bond number. The dimensionless contact radius is proportional to the fourth root of the magnetic bond number. The dimensionless height scales with the inverse square root of the magnetic Bond number. In the case of a moving marble dragged by a permanent magnet, the deformation is evaluated as the difference between advancing and receding curvatures of the top view. The dimensionless height and the contact diameter of the marble do not significantly depend on the speed or the capillary number. The scaling analysis and experimental data show that the deformation is proportional to the capillary number. PMID:24164113

Nguyen, Nam-Trung

2013-11-12

292

Theory and simulation of anisotropic pair correlations in ferrofluids in magnetic fields.

Anisotropic pair correlations in ferrofluids exposed to magnetic fields are studied using a combination of statistical-mechanical theory and computer simulations. A simple dipolar hard-sphere model of the magnetic colloidal particles is studied in detail. A virial-expansion theory is constructed for the pair distribution function (PDF) which depends not only on the length of the pair separation vector, but also on its orientation with respect to the field. A detailed comparison is made between the theoretical predictions and accurate simulation data, and it is found that the theory works well for realistic values of the dipolar coupling constant (? = 1), volume fraction (? ? 0.1), and magnetic field strength. The structure factor is computed for wavevectors either parallel or perpendicular to the field. The comparison between theory and simulation is generally very good with realistic ferrofluid parameters. For both the PDF and the structure factor, there are some deviations between theory and simulation at uncommonly high dipolar coupling constants, and with very strong magnetic fields. In particular, the theory is less successful at predicting the behavior of the structure factors at very low wavevectors, and perpendicular Gaussian density fluctuations arising from strongly correlated pairs of magnetic particles. Overall, though, the theory provides reliable predictions for the nature and degree of pair correlations in ferrofluids in magnetic fields, and hence should be of use in the design of functional magnetic materials. PMID:22612098

Elfimova, Ekaterina A; Ivanov, Alexey O; Camp, Philip J

2012-05-21

293

We present Brownian dynamics simulations of real charge-stabilized ferrofluids, which are stable colloidal dispersions of magnetic nanoparticles, with and without the presence of an external magnetic field. The colloidal suspensions are treated as collections of monodisperse spherical particles, bearing point dipoles at their centers and undergoing translational and rotational Brownian motions. The overall repulsive isotropic interactions between particles, governed by electrostatic repulsions, are taken into account by a one-component effective pair interaction potential. The potential parameters are fitted in order that computed structure factors are close to the experimental ones. Two samples of ferrofluid differing by the particle diameter and consequently by the intensity of the magnetic interaction are considered here. The magnetization and birefringence curves are computed: a deviation from the ideal Langevin behaviors is observed if the dipolar moment of particles is sufficiently large. Structure factors are also computed from simulations with and without an applied magnetic field H: the microstructure of the repulsive ferrofluid becomes anisotropic under H. Even our simple modeling of the suspension allows us to account for the main experimental features: an increase of the peak intensity is observed in the direction perpendicular to the field whereas the peak intensity decreases in the direction parallel to the field. PMID:15367036

Mériguet, G; Jardat, M; Turq, P

2004-09-22

294

Thermal Marangoni instability and magnetic pressure for a thin ferrofluid layer.

We study the linear coupling between the Marangoni and Cowley-Rosensweig instabilities for a thin layer of ferrofluid subjected to a temperature gradient and a magnetic field. Both are perpendicular to the reference horizontal boundaries, one of which is a rigid plate, while the other is a free surface remaining flat as long as the magnetic field is smaller than the critical value of the onset of the static isothermal Cowley-Rosensweig instability. Our study considers at first a ferrofluid layer resting on the rigid border. In the stationary case, when heating is directed from the rigid side, a magnetic field, smaller than the Cowley-Rosensweig critical one, can induce a new pattern: the critical Marangoni number is much lower than in the nonmagnetic undeformable case, for a dimensionless wavenumber of O(square root Bo) less than 1.992, its Newtonian classical value. When heating from the gaseous phase, an oscillatory marginal case exists theoretically, but for unphysical conditions. We consider also the case when the ferrofluid is hanging down from the rigid side. Only the wavelength critical value of the Rayleigh-Taylor instability that separates a stable region from an unstable one changes. PMID:19426330

Hennenberg, Marcel; Slavtchev, Slavtcho; Weyssow, Boris

2009-04-01

295

Extensions of Classical Hydrodynamics

NASA Astrophysics Data System (ADS)

An abstract dynamical system is formulated from three features extracted from classical hydrodynamics. One its particular realization is then the classical hydrodynamics, other possible realizations are extensions of the classical hydrodynamics. The three features entering the formulation of the abstract dynamical system are the conservation laws, the compatibility with equilibrium thermodynamics, and the compatibility with classical mechanics in the limit of no dissipation. The particular extensions on which we illustrate the process of constructing different realizations are those arising when dealing with fluids in the vicinity of gas-liquid phase transitions (i.e. fluids involving large spatial inhomogeneities and large fluctuations).

Grmela, Miroslav

2008-08-01

296

Lagrange hydrodynamics as extended Euler hydrodynamics: Hamiltonian and GENERIC structures

NASA Astrophysics Data System (ADS)

The extended Euler hydrodynamics proposed in Phys. Rev. Lett. 84 (2000) 3228 as hydrodynamics with correct solid limit is interpreted as a reconstruction of Lagrange hydrodynamics in the Eulerian setting. The geometrical formulation of the classical Euler and the classical Navier-Stokes-Fourier hydrodynamics is shown to be applicable also to the extended theory.

Grmela, Miroslav

2002-04-01

297

Combustion Hydrodynamics and Chemistry.

National Technical Information Service (NTIS)

Accomplishments in combustion hydrodynamics and chemistry studies consisted of a computational study of the chemical kinetics of hydrogen combustion along with some subsidiary studies and programming. Comparisons with experimental results have been genera...

E. Hyman

1981-01-01

298

Quantum Hydrodynamic Equations

In the previous chapters, we have derived quantum macroscopic models from a Wigner–Boltzmann equation using a diffusion scaling.\\u000a In this chapter, we show that, in analogy to the semi-classical situation, quantum hydrodynamic models can be derived by employing\\u000a a hydrodynamic scaling. We present two derivations: one from the (mixed-state) Schrödinger equation and one from a Wigner–Boltzmann\\u000a equation. This approach can

Ansgar Jüngel

299

Geometries and flows in optical hydrodynamics

NASA Astrophysics Data System (ADS)

The nature of light propagation suggests its correspondence to many universal problems in wave physics. Considering the complexity in many wave systems and taking advantage of optical systems which allow easy control of the input and direct imaging of the output, we treat nonlinear optics within the broader context in connection with general wave dynamic problems. This thesis presents experimental and theoretical work probing physics into the crossover between nonlinear optics and fluid dynamics. The main theme of the thesis concerns three aspects. First, we develop the fundamental model of optical hydrodynamics and use the model to demonstrate all-optical dispersive shockwaves, hydrodynamic instabilities, as well as spatial supercontinuum generation. Second, we control 'light flow' propagation by adding it into optically induced structures. This leads to the observation of nonlinear wave propagations in periodic, rotating and fractal potentials. Wave dynamics and energy transfer are dramatically different from those in homogeneous media. Finally, we shape the 'light flow' itself to observe the interactions between wave evolution and nonlinearity. The realization of diffraction-free Airy beam in nonlinear material provides potential applications to novel photonic imaging devices.

Jia, Shu

300

Adaptive grid radiation hydrodynamics with TITAN

NASA Astrophysics Data System (ADS)

We have developed a code which solves the coupled sets of radiation transfer and fluid dynamics equations (time dependent in one spatial dimension) by employing a fully implicit adaptive grid procedure to detect, resolve, and track the relevant physical structures. We have formulated TITAN as a general purpose code, written it in a user friendly manner, and documented it in detail. This code is available to the (astrophysical) community for the application to a broad variety of computational problems both as a research and a teching tool. We demonstrate the code's power and versatility in a series of simple problems. They range from pure hydrodynamics tests (shock tubes and blast waves), via radiation transfer tests (radiative heating and cooling), to radiation hydrodynamics tests (radiative shocks and blast waves). These can be viewed as predecessors to a host of interesting astrophysical problems such as nova and supernova explosions and light curves, accretion onto compact objects, star formation, and stellar variability.

Gehmeyr, M.; Mihalas, D.

1994-10-01

301

Adaptive Grid Radiation Hydrodynamics with TITAN

NASA Astrophysics Data System (ADS)

TITAN solves the coupled sets of radiation transfer and fluid dynamics equations (time dependent in one spatial dimension) by employing a fully implicit adaptive grid procedure to detect, resolve, and track the relevant physical structures. TITAN is formulated as a general purpose code, written in a user friendly manner, and documented in detail. We intend to make TITAN available to the astrophysical community for the application to a broad variety of computational problems. We demonstrate TITAN's power and versatility in a series of simple problems. They range from pure hydrodynamics test (shock tubes and blast waves), via radiation transfer test (radiative heating and cooling), to radiation hydrodynamics tests (radiative shocks and blast waves). These can be viewed as predecessors to a host of interesting astrophysical problems such as nova and supernova explosions and light curves, accretion onto compact objects, star formation, and stellar variability.

Gehmeyr, M.; Mihalas, D.

1993-12-01

302

NASA Astrophysics Data System (ADS)

In this study, some stabilized magnetite based ferrofluids were synthesized using Dextran as a stabilizing agent. In order to achieve optimum experimental conditions for synthesizing ferrofluids as MRI contrast agents, the Taguchi method was used. This approach was employed to design and minimize the number of required experiments. By using the Taguchi orthogonal (L16) array, four parameters including solution temperature and alkalinity, reaction temperature and stirring rate were selected at four predetermined levels for 16 experiments. Synthesizing processes established based on this set of experimental conditions were carried out and the obtained ferrofluids were characterized using PCS, VSM, TEM and FT-IR techniques. The obtained results were used and analyzed through the Qualitek-4 software and the proposed optimum experimental conditions were used for synthesizing the desired sample. Finally, this sample was used as a potential MRI contrast agent for imaging lymph nodes.

Ahmadi, Reza; Hosseini, Hamid Reza Madaah

2013-04-01

303

Molecular quantum wakes in the hydrodynamic plasma waveguide in air

We demonstrate a modulated plasma guiding effect from the molecular alignment wakes in the hydrodynamic plasma waveguide. A properly time-delayed laser pulse can be spatially confined by the hydrodynamic expansion induced plasma waveguide of an advancing femtosecond laser pulse. The spatial confinement can be further strengthened or weakened by following the quantum wakes of the impulsively excited rotational wave packets of the molecules in the plasma waveguide.

Wu Jian; Cai Hua; Zeng Heping [State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062 (China); Milchberg, H. M. [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States)

2010-10-15

304

Test problems for radiation and radiation-hydrodynamics codes

NASA Technical Reports Server (NTRS)

A number of test problems for radiation and radiation-hydrodynamics computer codes are described. These include evolution to radiative equilibrium, cooling from radiative equilibrium, subcritical and supercritical radiating shocks, and a radiating blast wave in a power-law density distribution. For each test problem, example input parameters and plots of the results are presented. Some test problems for pure hydrodynamics are also suggested. The radiation-hydrodynamics code used to perform the example test problems and the equations it solves are described in some detail.

Ensman, Lisa

1994-01-01

305

Ion holes in the hydrodynamic regime in ultracold neutral plasmas

We describe the creation of localized density perturbations, or ion holes, in an ultracold neutral plasma in the hydrodynamic regime, and show that the holes propagate at the local ion acoustic wave speed. We also observe the process of hole splitting, which results from the formation of a density depletion initially at rest in the plasma. One-dimensional, two-fluid hydrodynamic simulations describe the results well. Measurements of the ion velocity distribution also show the effects of the ion hole and confirm the hydrodynamic conditions in the plasma.

McQuillen, P.; Castro, J.; Strickler, T.; Bradshaw, S. J.; Killian, T. C. [Department of Physics and Astronomy, Rice University, Houston, Texas 77005 (United States)

2013-04-15

306

Flux-limited diffusion in hydrodynamics

NASA Technical Reports Server (NTRS)

The radiation transport equation, correct to order v/c, is used to derive a flux limiter valid in high-velocity hydrodynamic flows. In the limit v = 0 the widely used result of Levermore and Pomraning (LP) (1982) is recovered. In the case of homologous flow (v varies as R) the LP result remains valid, but in the presence of shock waves and other nonhomologous flows differences may be large. We calculate the Eddington factors, which are significantly altered, and discuss the importance of having them possess the correct form in the presence of a shock wave, e.g., on the neutrino transport during the formation of a supernova.

Cooperstein, J.; Baron, E.

1992-01-01

307

NASA Astrophysics Data System (ADS)

A numerical inversion method known from the analysis of light scattering by colloidal dispersions is now applied to magnetization curves of ferrofluids. The distribution of magnetic particle sizes or dipole moments is determined without assuming that the distribution is unimodal or of a particular shape. The inversion method enforces positive number densities via a non-negative least squares procedure. It is tested successfully on experimental and simulated data for ferrofluid samples with known multimodal size distributions. The created computer program MINORIM is made available on the web.

van Rijssel, Jos; Kuipers, Bonny W. M.; Erné, Ben H.

2014-03-01

308

Solitary waves, solitons and related (nonlinear) waves in dissipative media

At the end of last century the 'solitary wave', the 'wave of translation' or The wave, was an exotic (and to some like Airy an impossible) object in wave theory. Lamb's treatise on Hydrodynamics, the 'bible' of the early part of this century did only mention it slightly although great minds as Lord Rayleigh and Boussinesq, and subsequently Korteweg and

POR MANUEL G. VELARDE

309

We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe3O4) isolated from Magnetospirillum magnetotacticum (MS-1). Although dipolar chains form in magnetic colloids in zero applied field, when dried upon substrates, the solvent front disorders nanoparticle aggregation. Using avidin-biotin functionalization of the particles and substrate, we generated self-assembled, linear chain motifs that resist solvent front disruption in zero-field. The engineered self-assembly process we describe here provides an approach for the creation of ordered magnetic structures that could impact fields ranging from micro-electro-mechanical systems development to magnetic imaging of biological structures.

Ruder, Warren C.; Hsu, Chia-Pei D.; Edelman, Brent D.; Schwartz, Russell; LeDuc, Philip R.

2012-01-01

310

Ag nanoplates and Fe(3)O(4) nanoparticle-based ferrofluids were utilized to fabricate a magnetic field controlled optic switch. The changing of light transmittance (LT) is caused by the rotation of Ag nanoplates, whose long axis always follows the orientation of external magnetic field to minimize the potential energy. The sensitivity of switching was optimized by choosing Ag nanoplates with appropriate size and concentration. The switching of transmission is proved to be fast and fully reversible. This phenomenon not only indicates an effective method to adjust the propagation of optical signals, but also reveals the possibility and great potential to develop magnetic controlled functional devices. PMID:22873949

Mao, Yiwu; Liu, Jing; Ge, Jianping

2012-09-11

311

Weakly nonlinear study of normal-field instability in confined ferrofluids.

Similar to the classic three-dimensional Rosensweig instability, a ferrofluid confined in a vertical Hele-Shaw cell subjected to an in-plane normal magnetic field develops a periodic array of peaked interfacial structures. We perform a weakly nonlinear analysis that is able to reproduce the morphology of such pattern formation phenomenon at lowest nonlinear order. A mode-coupling theory is applied to compare the early nonlinear evolution of the interface with static shapes obtained when relevant forces equilibrate. Our nonlinear results indicate that the time-evolving shapes tend to approach stable stationary solutions. PMID:21867300

Lira, Sérgio A; Miranda, José A

2011-07-01

312

NASA Astrophysics Data System (ADS)

We report homeotropic (HT) alignment of ferroelectric liquid crystal (FLC) doped with various concentrations of ferro-fluid (FF) without using any type of alignment layer. The FF induced HT alignment of FLC was found to be dependent on the doping concentration as revealed by optical micrographs, contact angle, and dielectric spectroscopy studies. Higher water contact angle of FF doped FLC films with respect to pure FLC film suggests higher surface energy of FF doped FLC than the surface energy of substrate. The physico-chemical mechanism together with steric model successfully explains the HT alignment of the studied FLC on the ITO substrate.

Joshi, Tilak; Singh, Shri; Choudhary, Amit; Pant, R. P.; Biradar, A. M.

2013-07-01

313

NASA Astrophysics Data System (ADS)

We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe3O4) isolated from Magnetospirillum magnetotacticum (MS-1). Although dipolar chains form in magnetic colloids in zero applied field, when dried upon substrates, the solvent front disorders nanoparticle aggregation. Using avidin-biotin functionalization of the particles and substrate, we generated self-assembled, linear chain motifs that resist solvent front disruption in zero-field. The engineered self-assembly process we describe here provides an approach for the creation of ordered magnetic structures that could impact fields ranging from micro-electro-mechanical systems development to magnetic imaging of biological structures.

Ruder, Warren C.; Hsu, Chia-Pei D.; Edelman, Brent D.; Schwartz, Russell; LeDuc, Philip R.

2012-08-01

314

NASA Astrophysics Data System (ADS)

The process was studied of preparation of oriented BaFe12O19 films via deposition of BaFe12O19 nanoparticles from a suspension in a magnetic field. The films' structural, microstructural and magnetic properties were investigated by X-ray diffraction, scanning electron microscopy and magnetic measurements. The influence was explored of the particles's agglomeration in the ferrofluid on the films' properties and microstructure. Using time delay deposition, we obtained thick films with a high degree of orientation and good density.

Kolev, S.; Koutzarova, T.

2014-05-01

315

Large and negative Goos-Hänchen shift with magneto-controllability based on a ferrofluid

NASA Astrophysics Data System (ADS)

We report on the Goos-Hänchen (GH) shift of a beam reflected from ferrofluids composed of Fe3O4 nanoparticles coated with Ag, based on the stationary-phase method. We found that both the magneto and structural approaches can effectively control the GH shift. In particular, a larger negative GH shift can be obtained by changing the external magnetic field and the volume factor. The magneto-controllable GH shift provides a possibility for obtaining a desirable GH shift in a fixed configuration.

Fu, Mengshi; Zhang, Yu; Wu, Jipeng; Dai, Xiaoyu; Xiang, Yuanjiang

2013-03-01

316

The structure of ferrofluids (magnetite in decahydronaphtalene) stabilized with saturated mono-carboxylic acids of different chain lengths (lauric, myristic, palmitic and stearic acids) is studied by means of magnetization analysis and small-angle neutron scattering. It is shown that in case of saturated acid surfactants, magnetite nanoparticles are dispersed in the carrier approximately with the same size distribution whose mean value and width are significantly less as compared to the classical stabilization with non-saturated oleic acid. The found thickness of the surfactant shell around magnetite is analyzed with respect to stabilizing properties of mono-carboxylic acids. PMID:19376524

Avdeev, M V; Bica, D; Vékás, L; Aksenov, V L; Feoktystov, A V; Marinica, O; Rosta, L; Garamus, V M; Willumeit, R

2009-06-01

317

NASA Astrophysics Data System (ADS)

We report an in-fiber magnetic field sensor based on magneto-driven optical loss effects, while being implemented in a ferrofluid infiltrated microstructured polymer optical fiber. We demonstrate that magnetic field flux changes up to 2000 gauss can be detected when the magnetic field is applied perpendicular to the fiber axis. In addition, the sensor exhibits high polarization sensitivity for the interrogated wavelengths, providing the possibility of both field flux and direction measurements. The underlying physical and guidance mechanisms of this sensing transduction are further investigated using spectrophotometric, light scattering measurements, and numerical simulations, suggesting photonic Hall effect as the dominant physical, transducing mechanism.

Candiani, A.; Argyros, A.; Leon-Saval, S. G.; Lwin, R.; Selleri, S.; Pissadakis, S.

2014-03-01

318

Hydrodynamics and universality in cold atomic gases

NASA Astrophysics Data System (ADS)

Recent flurry of experiments on out-of-equilibrium dynamics in cold gases (Bosonic and Fermionic) has raised great interest in understanding collective behaviour of interacting particles. Although the dynamics of interacting gases depends on many details of the system, a great insight can be obtained in a rather universal limit of weak non-linearity, dispersion and dissipation. In this limit, using a reductive perturbation method we map many hydrodynamic models relevant to cold atoms to well known chiral one-dimensional equations such as Korteweg-de Vries (KdV), Burgers, KdV-Burgers, and Benjamin-Ono equations. This mapping [1] of rather complicated hydrodynamic equations to known chiral one-dimensional equations is of great experimental and theoretical interest. For instance, this mapping gives a simple way to make estimates for original hydrodynamic equations and to study phenomena such as shock waves, solitons and the interplay between nonlinearity, dissipation and dispersion. All these phenomena have been observed in experiments and are the hallmarks of nonlinear hydrodynamics.[4pt] [1] M. Kulkarni, A. G. Abanov, Phys. Rev. A 86, 033614 (2012)

Abanov, Alexander; Kulkarni, Manas

2013-03-01

319

Hydrodynamic modulation voltammetry.

Highly efficient background-correction techniques applicable to voltammetric methods of trace analysis can be developed by modulating the convection rate of the solution at a solid electrode surface. The theoretical aspects, advantages, disadvantages, and analytical applications of the various batch and flow approaches to hydrodynamic modulation voltammetry are discussed, together with trends in future developments. PMID:18962941

Wang, J

1981-06-01

320

Skew resisting hydrodynamic seal

A novel hydrodynamically lubricated compression type rotary seal that is suitable for lubricant retention and environmental exclusion. Particularly, the seal geometry ensures constraint of a hydrodynamic seal in a manner preventing skew-induced wear and provides adequate room within the seal gland to accommodate thermal expansion. The seal accommodates large as-manufactured variations in the coefficient of thermal expansion of the sealing material, provides a relatively stiff integral spring effect to minimize pressure-induced shuttling of the seal within the gland, and also maintains interfacial contact pressure within the dynamic sealing interface in an optimum range for efficient hydrodynamic lubrication and environment exclusion. The seal geometry also provides for complete support about the circumference of the seal to receive environmental pressure, as compared the interrupted character of seal support set forth in U.S. Pat. Nos. 5,873,576 and 6,036,192 and provides a hydrodynamic seal which is suitable for use with non-Newtonian lubricants.

Conroy, William T. (Pearland, TX); Dietle, Lannie L. (Sugar Land, TX); Gobeli, Jeffrey D. (Houston, TX); Kalsi, Manmohan S. (Houston, TX)

2001-01-01

321

Hydrodynamics of Certain Animals.

National Technical Information Service (NTIS)

The report contains an evaluation of hydrodynamic qualities of the body form of different necters which is of interest from both the aspect of general nectonology as well as in the scope of bionics and an examination of the microrelief of the cycloid fish...

Y. G. Aleev

1972-01-01

322

Ferrofluid squeeze film in an axially undefined porous journal bearing was analyzed to determine its performance considering anisotropic permeability of the porous facing and slip velocity at the interface of porous matrix and film region using Jenkins flow model. Expressions were obtained for dimensionless pressure, load capacity and response time of the squeeze film. How to deduce results for no-slip

Rajesh C Shah; M. V. Bhat

2004-01-01

323

A simple and low-cost colorimetric assay utilizing ferrofluidic nanoparticulate probes (FNPs) and a ligase for single-nucleotide polymorphism genotyping is described. Excellent sensitivity and selectivity were accomplished through the engagement of the FNPs and a ligase chain reaction. PMID:23923128

Shen, Wei; Lim, Cai Le; Gao, Zhiqiang

2013-09-21

324

A study is conducted on the influence of magnetic fields on the flow behavior of two ferrofluids with different levels of interparticle interaction, determined by prior rheological measurements. A Taylor-Couette system is used as a model for the investigations. A homogeneous magnetic field is applied in axial and transverse direction relative to the rotational axis of the system. The results

M. Reindl; S. Odenbach

2011-01-01

325

Symposium on Naval Hydrodynamics (10th), Hydrodynamics for Safety Fundamental Hydrodynamics.

National Technical Information Service (NTIS)

Partial Contents: Hydrodynamics for Safety/Maneuvering -- Effects of beam on the hydrodynamic characterisitcs of ship hulls; Bank effects on a ship moving through a short dredged channel, Double-body flow theory, Oscillatory testing for assessment of ship...

R. D. Cooper S. W. Doroff

1974-01-01

326

National Technical Information Service (NTIS)

Our work is in two areas: compressible nonlinear hydrodynamics and radiative shocks. Compressible nonlinear hydrodynamics has been the most productive area to date in the emerging field of Experimental Astrophysics. This is a natural area of research for ...

R. P. Drake

2003-01-01

327

NASA Astrophysics Data System (ADS)

Focusing particles and cells into a tight stream is often required in order for continuous flow detection, counting and sorting. So far a variety of particle focusing methods have been developed in microfluidic devices, among which magnetic focusing is still relatively new. We develop in this work an approach to embedding symmetrically two repulsive permanent magnets about a straight rectangular microchannel in a PDMS-based microfluidic device. The closest distance between the magnets is limited only by the sizes of the embedded and holder magnets involved in the fabrication process. The developed device is used to implement and investigate the three-dimensional magnetic focusing of polystyrene particles in ferrofluid microflow with both the top- and side-view visualizations. The effects of flow speed and particle size on the particle focusing effectiveness are studied. The developed device is also applied to magnetically focus yeast cells in ferrofluid, which proves to be biocompatible as verified by a cell viability test. In addition, an analytical model is developed and found to be able to predict the experimentally observed particle and cell focusing behaviors with reasonable agreement.

Zeng, Jian; Chen, Chen; Vedantam, Pallavi; Brown, Vincent; Tzeng, Tzuen-Rong J.; Xuan, Xiangchun

2012-10-01

328

In the present study, the permeability of 11 different iron oxide nanoparticle (IONP) samples (eight fluids and three powders) was determined using an in vitro blood–brain barrier model. Importantly, the results showed that the ferrofluid formulations were statistically more permeable than the IONP powder formulations at the blood–brain barrier, suggesting a role for the presently studied in situ synthesized ferrofluid formulations using poly(vinyl) alcohol, bovine serum albumin, collagen, glutamic acid, graphene, and their combinations as materials which can cross the blood–brain barrier to deliver drugs or have other neurological therapeutic efficacy. Conversely, the results showed the least permeability across the blood–brain barrier for the IONP with collagen formulation, suggesting a role as a magnetic resonance imaging contrast agent but limiting IONP passage across the blood–brain barrier. Further analysis of the data yielded several trends of note, with little correlation between permeability and fluid zeta potential, but a larger correlation between permeability and fluid particle size (with the smaller particle sizes having larger permeability). Such results lay the foundation for simple modification of iron oxide nanoparticle formulations to either promote or inhibit passage across the blood–brain barrier, and deserve further investigation for a wide range of applications.

Hoff, Dan; Sheikh, Lubna; Bhattacharya, Soumya; Nayar, Suprabha; Webster, Thomas J

2013-01-01

329

In the present study, the permeability of 11 different iron oxide nanoparticle (IONP) samples (eight fluids and three powders) was determined using an in vitro blood-brain barrier model. Importantly, the results showed that the ferrofluid formulations were statistically more permeable than the IONP powder formulations at the blood-brain barrier, suggesting a role for the presently studied in situ synthesized ferrofluid formulations using poly(vinyl) alcohol, bovine serum albumin, collagen, glutamic acid, graphene, and their combinations as materials which can cross the blood-brain barrier to deliver drugs or have other neurological therapeutic efficacy. Conversely, the results showed the least permeability across the blood-brain barrier for the IONP with collagen formulation, suggesting a role as a magnetic resonance imaging contrast agent but limiting IONP passage across the blood-brain barrier. Further analysis of the data yielded several trends of note, with little correlation between permeability and fluid zeta potential, but a larger correlation between permeability and fluid particle size (with the smaller particle sizes having larger permeability). Such results lay the foundation for simple modification of iron oxide nanoparticle formulations to either promote or inhibit passage across the blood-brain barrier, and deserve further investigation for a wide range of applications. PMID:23426527

Hoff, Dan; Sheikh, Lubna; Bhattacharya, Soumya; Nayar, Suprabha; Webster, Thomas J

2013-01-01

330

The use of genetically modified organisms (GMOs) as food and in food products is becoming more and more widespread. Polymerase chain reaction (PCR) technology is extensively used for the detection of GMOs in food products in order to verify compliance with labeling requirements. In this paper, we present a novel close-loop ferrofluid-driven PCR microchip for rapid amplification of GMOs. The microchip was fabricated in polymethyl methacrylate by CO2 laser ablation and was integrated with three temperature zones. PCR solution was contained in a circular closed microchannel and was driven by magnetic force generated by an external magnet through a small oil-based ferrofluid plug. Successful amplification of genetically modified soya and maize were achieved in less than 13 min. This PCR microchip combines advantages of cycling flexibility and quick temperature transitions associated with two existing microchip PCR techniques, and it provides a cost saving and less time-consuming way to conduct preliminary screening of GMOs. PMID:19399482

Sun, Yi; Kwok, Yien-Chian; Foo-Peng Lee, Peter; Nguyen, Nam-Trung

2009-07-01

331

NASA Astrophysics Data System (ADS)

The pair distribution function g( r) for a ferrofluid modeled by a bidisperse system of dipolar hard spheres is calculated. The influence of an external uniform magnetic field and polydispersity on g( r) and the related structure factor is studied. The calculation is performed by diagrammatic expansion methods within the thermodynamic perturbation theory in terms of the particle number density and the interparticle dipole-dipole interaction strength. Analytical expressions are provided for the pair distribution function to within the first order in number density and the second order in dipole-dipole interaction strength. The constructed theory is compared with the results of computer (Monte Carlo) simulations to determine the range of its validity. The scattering structure factor is determined using the Fourier transform of the pair correlation function g( r) - 1. The influence of the granulometric composition and magnetic field strength on the height and position of the first peak of the structure factor that is most amenable to an experimental study is analyzed. The data obtained can serve as a basis for interpreting the experimental small-angle neutron scattering results and determining the regularities in the behavior of the structure factor, its dependence on the fractional composition of a ferrofluid, interparticle correlations, and external magnetic field.

Nekhoroshkova, Yu. E.; Goldina, O. A.; Camp, P. J.; Elfimova, E. A.; Ivanov, A. O.

2014-03-01

332

We review the use of Monte Carlo simulations in the description of magnetic nanoparticles dispersed in a liquid carrier. Our main focus is the use of theory and simulation as tools for the description of the properties of ferrofluids. In particular, we report on the influence of polydispersity and short-range interaction on the self-organization of nanoparticles. Such contributions are shown to be extremely important for systems characterized by particles with diameters smaller than 10nm. A new 3D polydisperse Monte Carlo implementation for biocompatible magnetic colloids is proposed. As an example, theoretical and simulation results for an ionic-surfacted ferrofluid dispersed in a NaCl solution are directly compared to experimental data (transmission electron microscopy - TEM, magneto-transmissivity, and electron magnetic resonance - EMR). Our combined theoretical and experimental results suggest that during the aging process two possible mechanisms are likely to be observed: the nanoparticle's grafting decreases due to aggregate formation and the Hamaker constant increases due to oxidation. In addition, we also briefly discuss theoretical agglomerate formation models and compare them to experimental data. PMID:23360743

Bakuzis, Andris Figueiroa; Branquinho, Luis César; e Castro, Leonardo Luiz; e Eloi, Marcos Tiago de Amaral; Miotto, Ronei

2013-05-01

333

Ferrofluid based dispersive-solid phase extraction for spectrophotometric determination of dyes.

For the first time, ferrofluid based dispersive-solid phase extraction (D-SPE) has been applied for determination of trace levels of dyes in aqueous and fish samples. The contaminant used as a model compound was crystal violet (CV), a cationic dye, and was preconcentrated without any derivatization or ion-pair formation. The method is based on rapid injection of ferrofluid into the aqueous sample by a syringe. The sample preparation time is decreased by the fact that the sorbent dispersed in the bulk solution and extraction can be achieved very fast. In this way, the separation of sorbent from the aqueous bulk was achieved by a magnet, and no centrifugation is required. These significant features which obtained with this method are of key interest for routine trace laboratory analysis. The influence of different variables on D-SPE was investigated. Under optimum conditions, the calibration graph was linear over the range of 3.3-90 ?g L(-1), and the enrichment factor (EF) 267 was obtained. Detection limit was 1.51 ?g L(-1) (n=7), and the relative standard deviation of 5.6% at 50 ng mL(-1) was obtained (n=7). The proposed method was successfully applied for the determination of crystal violet in various samples. PMID:23849184

Davudabadi Farahani, Malihe; Shemirani, Farzaneh

2013-10-01

334

Nonlinear theory of pattern formation in ferrofluid films at high field strengths.

When a magnetic field is applied to a thin layer of a suspension of magnetic nanoparticles (ferrofluid), the formation of labyrinthine and hexagonal patterns is observed. We introduce a theory to describe ferrofluid patterns at high field, where a nonlinear relationship between field and magnetization is expected. The computational difficulties due to the use of a nonlinear magnetization curve are solved by a reformulation of the magnetic energy equation. The evolution of the pattern size at intermediate and very high fields can be understood by an analysis of limiting cases of the magnetization curve. In particular, at a very high field the pattern size reaches a constant saturation value which has been recently confirmed by experiments. The field for the onset of a nonlinear behavior is shifted to higher field strength due to a demagnetization effect. This can partially explain the ability of linear approaches to reproduce experimental data even at a high field. Finally, the impact of the nonlinearity of the magnetization curve on the transition between hexagonal and labyrinthine patterns is discussed. PMID:14995709

Richardi, J; Pileni, M P

2004-01-01

335

NASA Astrophysics Data System (ADS)

We have investigated the aggregation and dissociation dynamics of 6-nm size Fe3O4 nanoparticles coated by tetra methyl ammonium hydroxide (TMAH) and the same size ?-Fe2O3 nanoparticles precipitated inside an alginate hydrogel matrix, both in aqueous suspensions, using dc magnetic-field-induced time-dependent light scattering patterns. For the Fe3O4 ferrofluid, a strong anisotropy in light scattering was observed for light propagating perpendicular to the magnetic field. This behavior is attributed to the aggregation of the nanoparticles into chain-like and column-like structures oriented parallel to the magnetic field. A significantly different behavior is observed for the aqueous suspension of ?-Fe2O3 nanoparticles precipitated in alginate hydrogel, for which the application of the dc magnetic field produced little to no change in the light scattering patterns. We attribute this difference to the constrained random distribution of ?-Fe2O3 nanoparticles precipitated in the alginate matrix. Correlating the results from this investigation with our previous study of magneto-thermal measurements in ac fields [Vaishnava et al., J. Appl. Phys. 102, 063914 (2007)], we conclude that for a ferrofluid to exhibit significant thermal effects under an ac magnetic field, it should exhibit optical anisotropy by developing a chain like structure under the influence of a dc magnetic field.

Rablau, Corneliu; Vaishnava, Prem; Sudakar, Chandran; Tackett, Ronald; Lawes, Gavin; Naik, Ratna

2008-08-01

336

Protein-polymer functionalized aqueous ferrofluids showing high T2 relaxivity.

Controlled size, shape and dispersibility of superparamagnetic iron oxide nanoparticles (SPIONs), has been achieved in a protein-polymer colloidal dispersion. Stable ferrofluid (FF) is synthesized in an aqueous medium of collagen, bovine serum albumin and poly(vinyl) alcohol that equilibrates with time, at ambient conditions, into an organized matrix with iron oxide particles sterically caged at defined sites. It mimics a biomineralization system; hence the process is termed biomimetics. Though the exact mechanism is not understood at this stage, we have established, with serial dilution of the protein-polymer solution that the SPIONs are formed inside the self-contained clusters of the two proteins and the polymer, which show a tendency to self assemble. More than the interparticle dipolar attractions of magnetic particles, electrostatic interactions play a role in cluster formation and collagen is responsible for the overall stability, supported by systematic dynamic light scattering data. The basic aim of this study was to increase magnetization of a previously synthesized ferrofluid without hampering stability, by reducing the total macromolecular concentration. Thrice the magnetization was achieved and in addition, the synthesized FFs exhibited very high transverse relaxivity and showed good contrast in mice liver, in the in vivo studies. PMID:24734534

Bhattacharya, S; Sheikh, L; Tiwari, V; Ghosh, M; Patel, J N; Patel, A B; Nayar, S

2014-05-01

337

The Evolution of Field-Induced Structure of Confined Ferrofluid Emulsions

NASA Astrophysics Data System (ADS)

We report a real-time study of the evolution of the structure of confined ferrofluid emulsions during the "liquid-solid" phase transition. A monodisperse oil-in-water ferrofluid emulsion is used. The structure evolution of the emulsion after rapidly applying a magnetic field is probed by the static light scattering. The scattering pattern exhibits pronounced rings reflecting the formation of chains and their coalescence to columns or even "worm" structures. The scattering ring is found to decrease in size and brighten in intensity with time. To monitor the structure evolution in time, both the ring peak position in scattering wavevector, qmax, and the peak intensity, Imax, are measured as a function of time. Both qmax and Imax saturate in less than 0.5 seconds after applying a magnetic field. At a constant cell thickness of 25 µm, the evolution of structure is essentially independent of volume fraction ranging from 0.015 to 0.13. In addition, a very good scaling is found in the scattered light intensity as a function of the scattering wavevector.

Mou, T.; Flores, G. A.; Liu, J.; Bibette, J.; Richard, J.

338

NASA Astrophysics Data System (ADS)

Microfluidic devices have been increasingly used in the past two decades for particle and cell manipulations in many chemical and biomedical applications. A variety of force fields have been demonstrated to control particle and cell transport in these devices including electric, magnetic, acoustic, and optical forces etc. Among these particle handling techniques, the magnetic approach provides clear advantages over others such as low cost, noninvasive, and free of fluid heating issues. However, the current knowledge of magnetic control of particle transport is still very limited, especially lacking is the handling of diamagnetic particle. This thesis is focused on the magnetic manipulation of diamagnetic particles and cells in ferrofluid flow through the use of a pair of permanent magnets. By varying the configuration of the two magnets, diverse operations of particles and cells is implemented in a straight microchannel that can potentially be integrated into lab-on-a-chip devices for various applications. First, an approach for embedding two, symmetrically positioned, repulsive permanent magnets about a straight rectangular microchannel in a PDMS-based microfluidic device is developed for particle focusing. Focusing particles and cells into a tight stream is often required in order for continuous detection, counting, and sorting. The closest distance between the magnets is limited only by the size of the magnets involved in the fabrication process. The device is used to implement and investigate the three-dimensional magnetic focusing of polystyrene particles in ferrofluid microflow with both top-view and side-view visualizations. The effects of flow speed and particle size on the particle focusing effectiveness are studied. This device is also applied to magnetically focus yeast cells in ferrofluid, which proves to be biocompatible as verified by cell viability test. In addition, an analytical model is developed and found to be able to predict the experimentally observed particle and cell focusing behaviors with reasonable agreement. Next, a simple magnetic technique to concentrate polystyrene particles and live yeast cells in ferrofluid flow through a straight rectangular microchannel is developed. Concentrating particles to a detectable level is often necessary in many applications. The magnetic field gradient is created by two attracting permanent magnets that are placed on the top and bottom of the planar microfluidic device and held in position by their natural attractive force. The effects of flow speed and magnet-magnet distance are studied and the device was applied for use for concentrating live yeast cells. The magnet-magnet distance is mainly controlled by the thickness of the device substrate and can be made small, providing a locally strengthened magnetic field as well as allowing for the use of dilute ferrofluid in the developed magnetic concentration technique. This advantage not only enables a magnetic/fluorescent label-free handling of diamagnetic particles but also renders such handling biocompatible. Lastly, a device is presented for a size-based continuous separation of particles through a straight rectangular microchannel. Particle separation is critical in many applications involving the sorting of cells. A first magnet is used for focusing the particle mixture into a single stream due to its relative close positioning with respect to the channel, thus creating a greater magnetic field magnitude. Then, a following magnet is used to displace the aligned particles to dissimilar flow paths by placing it farther away compared the first magnet, which provides a weaker magnetic field, therefore more sensitive towards the deflection of particles based on their size. The effects of both flow speed and separator magnet position are examined. The experimental data are found to fit well with analytical model predictions. This is followed by a study replacing the particles which are closely sized to that of live yeast cells and observe the separation of the cells from larger particles. Afterwards, a test for

Zeng, Jian

339

Self-assembled magnetic colloidal suspensions are sought after by material scientists owing to its huge application potential. The biomedical applications of colloidal nanoparticles necessitate that they are biocompatible, non-interacting, monodispersed and hence the synthesis of such nanostructures has great relevance in the realm of nanoscience. Silica-coated superparamagnetic iron oxide nanoparticles based ferrofluids were prepared using polyethylene glycol as carrier fluid by employing a controlled co-precipitation technique followed by a modified sol-gel synthesis. A plausible mechanism for the formation of stable suspension of SiO2-coated Iron Oxide nanoparticles with a size of about 9 nm dispersed in polyethylene glycol (PEG) is proposed. Core-shell nature of the resultant SiO2-Iron Oxide nanocomposite was verified using transmission electron microscopy. Fourier transform-infrared spectroscopy studies were carried out to understand the structure and nature of chemical bonds. The result suggests that Iron Oxide exist in an isolated state inside silica matrix. Moreover, the presence of silanol bonds establishes the hydrophilic nature of silica shell confirming the formation of stable ferrofluid with PEG as carrier fluid. The magnetic characterization reveals the superparamagnetic behavior of the nanoparticles with a rather narrow distribution of blocking temperatures. These properties are not seen in ferrofluids prepared from Iron Oxide nanoparticles without SiO2 coating. The latter suggests the successful tuning of the inter-particle interactions preventing agglomeration of nanoparticles. Cytotoxicity studies on citric acid coated water based ferrofluid and silica-coated PEG-based ferrofluid were evaluated by 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium chloride assay and it shows an enhanced compatibility for silica modified nanoparticles. PMID:21449334

Narayanan, T N; Mary, A P Reena; Swalih, P K Anas; Kumar, D Sakthi; Makarov, D; Albrecht, M; Puthumana, Jayesh; Anas, Abdulaziz; Anantharaman, M R

2011-03-01

340

NASA Astrophysics Data System (ADS)

Ferrofluids containing nanoparticles of Mn0.5Zn0.5Fe2O4 (MZ5) and Fe3O4 (magnetite) have been examined as potential thermal transport media and energy harvesting materials. The ferrofluids were synthesized by chemical co-precipitation and characterized by EDX to determine composition and by TEM to determine particle size and agglomeration. A range of particle coatings and carrier fluids were used to complete the fluid preparation. Commercially available ferrofluids were tested in custom built rigs to demonstrate both thermal pumping (for waste heat removal applications) and power induction (for power conversion and energy harvesting applications). The results indicate that simple ferrofluids possess the necessary properties to remove waste heat, either into thermal storage or for conversion to electrical power.

Sansom, C. L.; Jones, P.; Dorey, R. A.; Beck, C.; Stanhope-Bosumpim, A.; Peterson, J.

2013-06-01

341

Radial hydrodynamics in risers

On the basis of the benchmark modeling exercise at Fluidization VIII, predicting riser hydrodynamics continues to be more of an art than a science. Ten different hydrodynamic models were compared with a set of experimental data that covered a wide range of operating conditions and showed reasonable to poor overall agreement. Herein, the authors describe the model that gave the best overall agreement with the experimental data. Density is calculated by a correlation based on slip factor, and the radial voidage profile depends solely on the cross-sectional average void fraction. Both the gas and velocity profile follows a power law type expression, the gas velocity at the wall is zero. The model predictions agree well with experiments conducted with sand but not as well as those conducted with fluidized catalytic cracking catalyst.

Godfroy, L.; Chaouki, J. [Ecole Polytechnique, Montreal, Quebec (Canada). Dept. of Chemical Engineering] [Ecole Polytechnique, Montreal, Quebec (Canada). Dept. of Chemical Engineering; Patience, G.S. [E.I. du Pont de Nemours and Co., Wilmington, DE (United States)] [E.I. du Pont de Nemours and Co., Wilmington, DE (United States)

1999-01-01

342

Landau hydrodynamics reexamined

NASA Astrophysics Data System (ADS)

We review the formulation of Landau hydrodynamics and find that the rapidity distribution of produced particles in the center-of-mass system should be more appropriately modified as dN/dy?exp{yb2-y2}, where yb=ln{sNN/mp} is the beam nucleon rapidity, instead of Landau's original distribution, dN/dy(Landau)?exp{L2-y2}, where L=ln{sNN/2mp}. The modified distribution agrees better with experimental dN/dy data than the original Landau distribution and can be represented well by the Gaussian distribution, dN/dy(Gaussian)?exp{-y2/2L}. Past successes of the Gaussian distribution in explaining experimental rapidity data can be understood, not because it is an approximation of the original Landau distribution, but because it is in fact a close representation of the modified distribution. Predictions for pp and AA collisions at LHC energies in Landau hydrodynamics are presented.

Wong, Cheuk-Yin

2008-11-01

343

NSDL National Science Digital Library

Hydrodynamics and viscosity: This site contains a complete description of fluid properties and fluid mechanics by defining the nature of a fluid, show where fluid mechanics concepts are common with those of solid mechanics and indicate some fundamental areas of difference, introduce viscosity and show what are Newtonian and non-Newtonian fluids and define the appropriate physical properties and show how these allow differentiation between solids and fluids as well as between liquids and gases.

2008-09-22

344

Hydrodynamic microelectrode voltammetry

This review provides a detailed overview of the progress made in the last 25 years in the field of hydrodynamic microelectrodes\\u000a (HMEs) with particular application to the study of electrochemical kinetics. A survey is made of the various types of HMEs\\u000a that have been reported in the literature, with summaries of theoretical and experimental details along with the results published

N. V. Rees; R. G. Compton

2008-01-01

345

Temporal and spatial dependence of hydrodynamic correlations: Simulation and experiment

NASA Astrophysics Data System (ADS)

Time-dependent hydrodynamic interactions in a colloidal suspension of hard spheres are studied, both experimentally and through computer simulation. The focus is on the behavior at small wave vectors, which directly probes the temporal evolution of hydrodynamic interactions between nearby particles. The computer simulations show that the time-dependent diffusion coefficient has the same functional form for all wave vectors, with a single characteristic scaling time for each length scale and for each volume fraction. Wave-vector-averaged effective diffusion coefficients, measured experimentally using diffusing wave spectroscopy, also scale to the same functional form. In this case, the scaling time is dependent on both volume fraction and particle size; it decreases sharply with decreasing particle radius, reflecting the greater contribution from smaller wave vectors that is contained in the scattering from the smaller particles. For a direct comparison of simulation and experiment, we simulate the experimentally observed correlation functions, by averaging the wave-vector-dependent computer-simulation data with the weighting appropriate to the experimental technique. Although the overall scaling is similar, there are quantitative differences in the simulated and measured relaxation times. We suggest these differences are due to the compressibility of the suspension, and that the resultant pressure waves make an unexpectedly significant contribution to the hydrodynamic interactions. (c) 1995 The American Physical Society

Ladd, Anthony J. C.; Gang, Hu; Zhu, J. X.; Weitz, D. A.

1995-12-01

346

A saw having a self-pumped hydrodynamic blade guide or bearing for retaining the saw blade in a centered position in the saw kerf (width of cut made by the saw). The hydrodynamic blade guide or bearing utilizes pockets or grooves incorporated into the sides of the blade. The saw kerf in the workpiece provides the guide or bearing stator surface. Both sides of the blade entrain cutting fluid as the blade enters the kerf in the workpiece, and the trapped fluid provides pressure between the blade and the workpiece as an inverse function of the gap between the blade surface and the workpiece surface. If the blade wanders from the center of the kerf, then one gap will increase and one gap will decrease and the consequent pressure difference between the two sides of the blade will cause the blade to re-center itself in the kerf. Saws using the hydrodynamic blade guide or bearing have particular application in slicing slabs from boules of single crystal materials, for example, as well as for cutting other difficult to saw materials such as ceramics, glass, and brittle composite materials.

Blaedel, K.L.; Davis, P.J.; Landram, C.S.

2000-07-04

347

Hydrodynamics of fossil fishes.

From their earliest origins, fishes have developed a suite of adaptations for locomotion in water, which determine performance and ultimately fitness. Even without data from behaviour, soft tissue and extant relatives, it is possible to infer a wealth of palaeobiological and palaeoecological information. As in extant species, aspects of gross morphology such as streamlining, fin position and tail type are optimized even in the earliest fishes, indicating similar life strategies have been present throughout their evolutionary history. As hydrodynamical studies become more sophisticated, increasingly complex fluid movement can be modelled, including vortex formation and boundary layer control. Drag-reducing riblets ornamenting the scales of fast-moving sharks have been subjected to particularly intense research, but this has not been extended to extinct forms. Riblets are a convergent adaptation seen in many Palaeozoic fishes, and probably served a similar hydrodynamic purpose. Conversely, structures which appear to increase skin friction may act as turbulisors, reducing overall drag while serving a protective function. Here, we examine the diverse adaptions that contribute to drag reduction in modern fishes and review the few attempts to elucidate the hydrodynamics of extinct forms. PMID:24943377

Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert

2014-08-01

348

A saw having a self-pumped hydrodynamic blade guide or bearing for retaining the saw blade in a centered position in the saw kerf (width of cut made by the saw). The hydrodynamic blade guide or bearing utilizes pockets or grooves incorporated into the sides of the blade. The saw kerf in the workpiece provides the guide or bearing stator surface. Both sides of the blade entrain cutting fluid as the blade enters the kerf in the workpiece, and the trapped fluid provides pressure between the blade and the workpiece as an inverse function of the gap between the blade surface and the workpiece surface. If the blade wanders from the center of the kerf, then one gap will increase and one gap will decrease and the consequent pressure difference between the two sides of the blade will cause the blade to re-center itself in the kerf. Saws using the hydrodynamic blade guide or bearing have particular application in slicing slabs from boules of single crystal materials, for example, as well as for cutting other difficult to saw materials such as ceramics, glass, and brittle composite materials.

Blaedel, Kenneth L. (Dublin, CA); Davis, Pete J. (Pleasanton, CA); Landram, Charles S. (Livermore, CA)

2000-01-01

349

Air-water two-phase flow approach to simulate nearshore wave motion

Wave breaking and wave runup have a major influence on nearshore hydrodynamics. Hydrodynamic characteristics of wave motions in the nearshore zone play a key role on the beach profile changes and their evolution. In the case of wave breaking, there is significant mixing of air and water at the wave crest, along with relatively high kinetic energy, so prediction of

Roham Bakhtyar; Amir Mehdi Razmi; David Andrew Barry

2010-01-01

350

Optical monitoring study on estuarine sediment incipient under marine hydrodynamic

NASA Astrophysics Data System (ADS)

For the deserted estuary without sediment inflow, ocean hydrodynamic has become the main force for coastal erosion. This paper utilizes wave-tide gauge and current meter to monitor the hydrodynamic within the experimental area and also, turbidity meter is used to conduct indirect monitoring to the sediment concentration (the corresponding relation between the turbidity value and the content of suspended particles in the water is pre-calibrated indoors). Statistical means is adopted to calculate the correlativity between the turbidity and hydropower factors, such as wave height, tide height and flow meter which are determined on site and then the determining factors for sediment incipient are obtained. The conclusion is that the eddy and turbulent flow caused by broken wave constitute the main dynamic factors for the sediment incipient and the incipient velocity mainly comes from the flow rate of the eddy and turbulence resulting from the broken wave.

Qin, Hao; Li, Shucai; Zhang, Lei

2009-12-01

351

Building a Hydrodynamics Code with Kinetic Theory

NASA Astrophysics Data System (ADS)

We report on the development of a test-particle based kinetic Monte Carlo code for large systems and its application to simulate matter in the continuum regime. Our code combines advantages of the Direct Simulation Monte Carlo and the Point-of-Closest-Approach methods to solve the collision integral of the Boltzmann equation. With that, we achieve a high spatial accuracy in simulations while maintaining computational feasibility when applying a large number of test-particles. The hybrid setup of our approach allows us to study systems which move in and out of the hydrodynamic regime, with low and high particle densities. To demonstrate our code's ability to reproduce hydrodynamic behavior we perform shock wave simulations and focus here on the Sedov blast wave test. The blast wave problem describes the evolution of a spherical expanding shock front and is an important verification problem for codes which are applied in astrophysical simulation, especially for approaches which aim to study core-collapse supernovae.

Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Pickett, Rodney; Strother, Terrance

2013-08-01

352

Computational Naval Ship Hydrodynamics

The primary purpose of our research efforts is to improve naval design and detection capabilities. Our current research efforts leverage high performance computing (HPC) resources to perform high-resolution numerical simulations with hundreds-of-millions to billions of unknowns to study wave breaking behind a transom stern, wave-impact loading, the generation of spray by high-speed planing craft, air entrainment by plunging breaking waves,

Kyle A. Brucker; Douglas G. Dommermuth; Thomas T. O'Shea; Dick K. P. Yue; Kelli Hendrickson; Gabriel Weymouth

2010-01-01

353

Operational oceanographic system for coastal hydrodynamics in Korea

NASA Astrophysics Data System (ADS)

We have developed an operational oceanographic system for the coastal waters of Korea using ROMS. The operational oceanographic modeling system consists of atmospheric and hydrodynamic models coupled with three-dimensional hydrodynamics, wave, sediment transport and water quality modules. We forecast the results two times a day in the 72 hours base including sea surface elevation, currents, temperature, salinity, and wave information etc. for the coastal waters of Korea. The predicted results are exported to the web-GIS based coastal information system for the application of various coastal activities and problems and the real-time dissemination to the public. The modeling system for the coastal waters of Korea uses operational ocean model ROMS coupled with wave model SWAN for the hydrodynamics and waves, meteorological model WRF for the atmospheric surface forcing, regional tide model NAO.99jb for the tides, and eutrophication model CE-QUAL-ICM for the water quality. The predicted results of WRF and ROMS for the Yellow Sae are nested for the boundary condition of the model. The model ROMS was calibrated with tidal surface data, then the model was verified with current data observed near the coastal waters of Korea with bottom mounted ADCP and AWAC. To validate the operational model we use real-time monitoring data obtained by Buoy, HF-Radar, stationary Satellite, and observatory tower system installed by KORDI and KHOA funded by Korean government for the observation of hydrodynamics in Korea. In this study, we have developed an operational oceanographic system for the coastal hydrodynamics in Korea. The operational model ROMS predicts the information of coastal waters of Korea twice a day for 72 hours. The predicted result is visualized effectively through the web-GIS system to provide predicted coastal hydrodynamics in Korea to the public. This high-resolution coastal operational oceanographic system will be used as a part of the development of Korea Operational Oceanographic System (KOOS) with other operational oceanographic system.

Lim, H.; Kim, C. S.; Park, K.

2011-12-01

354

Hydrodynamic damping contributions for an advanced floating production system design

Catenary moored floating vessels used for hydrocarbon production and storage exhibit low frequency, large amplitude resonant motions predominantly in the surge direction. These motions are caused by slow drift forces resulting primarily from random wave action. Accurate predictions of the damping forces are required in order to design fit for purpose moorings. This paper considers the contribution caused by hydrodynamic

D. T. Brown; J. Fang

1996-01-01

355

Fast lattice Boltzmann solver for relativistic hydrodynamics.

A lattice Boltzmann formulation for relativistic fluids is presented and numerically validated through quantitative comparison with recent hydrodynamic simulations of relativistic fluids. In order to illustrate its capability to handle complex geometries, the scheme is also applied to the case of a three-dimensional relativistic shock wave, generated by a supernova explosion, impacting on a massive interstellar cloud. This formulation opens up the possibility of exporting the proven advantages of lattice Boltzmann methods, namely, computational efficiency and easy handling of complex geometries, to the context of (mildly) relativistic fluid dynamics at large, from quark-gluon plasmas up to supernovae with relativistic outflows. PMID:20867451

Mendoza, M; Boghosian, B M; Herrmann, H J; Succi, S

2010-07-01

356

Basics of smoothed particle hydrodynamics

We present a review of the smoothed particle hydrodynamics (SPH) method and present several sample problems to illustrate its properties as a general purpose computational fluid dynamics technique. Accuracy and efficiency are also assessed. Our findings suggest that he SPH methods has great potential for development into an alternative to finite difference and finite element methods. The SPH method has received much less development effort than the others, but even in its present form it is a useful tool for getting approximate solutions to a wide variety of three-dimensional fluid dynamics problems at moderate computational cost. For some problems, it may prove to be the method of choice. However, for many problems, such as shock waves, better results may be obtained with more traditional finite difference methods. We also find that the method can generate unphysical solutions if not used with care, so careful comparison of solutions to experimental or analytical results for each class of problems is necessary. 26 refs., 21 figs.

Cloutman, L.D.

1990-05-01

357

Hydrodynamic cavitation for sonochemical effects

A comparative study of hydrodynamic and acoustic cavitation has been made on the basis of numerical solutions of the Rayleigh–Plesset equation. The bubble\\/cavity behaviour has been studied under both acoustic and hydrodynamic cavitation conditions. The effect of varying pressure fields on the collapse of the cavity (sinusoidal for acoustic and linear for hydrodynamic) and also on the latter’s dynamic behaviour

V. S. Moholkar; P. Senthil Kumar; A. B. Pandit

1999-01-01

358

EUNHA: a New Cosmological Hydrodynamic Simulation Code

NASA Astrophysics Data System (ADS)

We develop a parallel cosmological hydrodynamic simulation code designed for the study of formation and evolution of cosmological structures. The gravitational force is calculated using the TreePM method and the hydrodynamics is implemented based on the smoothed particle hydrodynamics. The initial displacement and velocity of simulation particles are calculated according to second-order Lagrangian perturbation theory using the power spectra of dark matter and baryonic matter. The initial background temperature is given by Recfast and the temperature fluctuations at the initial particle position are assigned according to the adiabatic model. We use a time-limiter scheme over the individual time steps to capture shock-fronts and to ease the time-step tension between the shock and preshock particles. We also include the astrophysical gas processes of radiative heating/cooling, star formation, metal enrichment, and supernova feedback. We test the code in several standard cases such as one-dimensional Riemann problems, Kelvin-Helmholtz, and Sedov blast wave instability. Star formation on the galactic disk is investigated to check whether the Schmidt-Kennicutt relation is properly recovered. We also study global star formation history at different simulation resolutions and compare them with observations.

Shin, Jihye; Kim, Juhan; Kim, Sungsoo S.; Park, Changbom

2014-06-01

359

Constraints on Rindler hydrodynamics

NASA Astrophysics Data System (ADS)

We study uncharged Rindler hydrodynamics at second order in the derivative expansion. The equation of state of the theory is given by a vanishing equilibrium energy density. We derive relations among the transport coefficients by employing two frameworks. First, by the requirement of having an entropy current with a non-negative divergence, second by studying the thermal partition function on stationary backgrounds. The relations derived by these two methods are equivalent. We verify the results by studying explicit examples in flat and curved space-time geometries.

Meyer, Adiel; Oz, Yaron

2013-07-01

360

In situ imaging of field-induced hexagonal columns in magnetite ferrofluids.

Field-induced structures in a ferrofluid with well-defined magnetite nanoparticles with a permanent magnetic dipole moment are analyzed on a single-particle level by in situ cryogenic transmission electron microscopy (2D). The field-induced columnar phase locally exhibits hexagonal symmetry and confirms the structures observed in simulations for ferromagnetic dipolar fluids in 2D. The columns are distorted by lens-shaped voids, due to the weak interchain attraction relative to field-directed dipole-dipole attraction. Both dipolar coupling and the dipole concentration determine the dimensions and the spatial arrangement of the columns. Their regular spacing manifests long-range end-pole repulsions that eventually dominate the fluctuation-induced attractions between dipole chains that initiate the columnar transition. PMID:17155554

Klokkenburg, Mark; Erné, Ben H; Meeldijk, Johannes D; Wiedenmann, Albrecht; Petukhov, Andrei V; Dullens, Roel P A; Philipse, Albert P

2006-11-01

361

The influence of particle size on the magnetorheological properties of an inverse ferrofluid

NASA Astrophysics Data System (ADS)

The dependence of magnetorheological properties on particle size is studied, using a model magnetorheological fluid consisting of nonmagnetic silica particles suspended in a ferrofluid. For small particles a strong increase of magnetorheological properties with particle size was found. At a certain particle size and field strength a crossover occurs to a regime where there is only a very limited size dependence. This can be understood in terms of the length of the chains in relation to the gap size of the geometry. Crossover occurs when the average chain length becomes comparable to the gap size. The remaining size dependence may be explained by polydispersity, variations in the morphology, variations in the sterically stabilizing layer of the particles and surface roughness of the geometry.

de Gans, B. J.; Duin, N. J.; van den Ende, D.; Mellema, J.

2000-08-01

362

Entrainment by a rotating magnetic field of a ferrofluid contained in a cylinder.

Entrainment by a rotating magnetic field of a ferrofluid contained in a cylinder is studied on the basis of spin-diffusion theory. The equations for flow velocity and spin velocity, coupled to Maxwell's equations of magnetostatics, are solved in first-harmonic approximation under the assumption that the magnetic field is small compared to the saturation magnetization. The solution leads to a coupled set of nonlinear integral equations, which can be solved numerically by iteration in a recursive scheme by use of the analytic lowest order perturbation theory solution as the initial state. At a critical applied field, the recursive scheme shows bifurcation. At sufficiently high field, the solution with the lower rate of dissipation shows flow in the direction opposite to the rotating applied field. PMID:21929095

Felderhof, B U

2011-08-01

363

In this study, the composite magnetic nanoparticles of coated SiO nano film with about 8 nm size and high saturation magnetization value, were synthesized by liquid phase precipitation method. The magnetic nanoparticles can be dispersed in various liquid media, widely known as magnetic fluids or ferrofluids with both magnetic and liquid properties. The materials been collected great interests and more and more attentions to focus into Drug Delivery System (DDS) as a new technology in this paper. We use the composite nanoparticles to disperse H2O and inject the solutions into rat's in-vivo organs. And, in the experiments by using a strong photon beam of SPring-8 Synchrotron Radiation facility, the distribution stat and the effects of magnetic field as well as drug delivery behaviour of nanoparticles in the rat' kidney are verified by the in-vivo observations. PMID:22400252

Ju, D Y; Bian, P; Kumazawa, T; Nakano, M; Matsuura, H; Umetani, K; Komdo, T; Uozumi, Y; Makino, K; Noda, N; Koide, K; Akutsu, M; Masuyama, K

2011-10-01

364

Effect of dimerization on the field-induced birefringence in ferrofluids.

The magnetic-field-induced birefringence in a ferrofluid composed of spherical cobalt nanoparticles has been studied both experimentally and theoretically. The considerable induced birefringence determined experimentally has been attributed to the formation of chains of nanoparticles. The birefringence has been measured as a function of the external magnetic field and the volume fraction (f) of nanoparticles. It is quadratic in f as opposed to the Faraday effect, which is linear in f. Experimental results agree well with the theoretical model based on a simple density functional approach. For dilute solutions the experimental results can be explained by assuming that only dimers of nanoparticles are formed while the concentration of longer chains is negligible. PMID:23848690

Szczytko, Jacek; Vaupoti?, Nataša; Osipov, Mihail A; Madrak, Karolina; Górecka, Ewa

2013-06-01

365

We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe(3)O(4)) isolated from Magnetospirillum magnetotacticum (MS-1). Although dipolar chains form in magnetic colloids in zero applied field, when dried upon substrates, the solvent front disorders nanoparticle aggregation. Using avidin-biotin functionalization of the particles and substrate, we generated self-assembled, linear chain motifs that resist solvent front disruption in zero-field. The engineered self-assembly process we describe here provides an approach for the creation of ordered magnetic structures that could impact fields ranging from micro-electro-mechanical systems development to magnetic imaging of biological structures. PMID:22952408

Ruder, Warren C; Hsu, Chia-Pei D; Edelman, Brent D; Schwartz, Russell; Leduc, Philip R

2012-08-01

366

We report an experimental investigation of time dependent anisotropic light scattering by an aqueous suspension of tetramethyl ammonium hydroxide coated Fe3O4 nanoparticles (approximately 6 nm) under the ON-OFF transient of an external dc magnetic field. The study employs the synchronized recording and measurement of the two magnetic-field-induced light-scattering patterns produced by two identical orthogonal He-Ne laser beams passing through the ferrofluid sample and propagating parallel and perpendicular to the applied field, respectively. From these patterns, we extract the time dependence of the induced optical anisotropy, which provides a measure of the characteristic time scale and kinematic response for field-induced structure formation in the sample. We propose that the time evolution of the scattering patterns, which is very fast at short times and significantly slower at long times, can be explained using a model based on a two-stage chain formation and coarsening processes. PMID:19113131

Rablau, Corneliu; Vaishnava, Prem; Sudakar, Chandran; Tackett, Ronald; Lawes, Gavin; Naik, Ratna

2008-11-01

367

Stochastic dynamics of superparamagnetic moments in polidisperse ferrofluids

NASA Astrophysics Data System (ADS)

In previous works, we studied the dynamics of the magnetic moments in ferrofluids te{schererBJP,scherer-matuttis, scherer-ricci}, and other authors have also dealt with this problem te{shliomis}. In our previous works also computational simulations have been performed. The present work differs from those in two important aspects: (i) the magnetic particles are not of uniform size, but have a lognormal distribution of diameters; (ii) the parameters used in the simulations, like magnetization, anisotropy constant, liquid viscosity, applied field, temperature, etc., correspond to the values for realistic ferrofluids (in the previous works we used values, which were convenient for the simulations). For this reason, we will briefly re-derive the equations of motion, keeping all the relevant constants in them. To avoid big powers of 10 in the simulations, we introduce an appropriate system of units. The equations of motion for the particles' rotation and for the rotation of their magnetic moments are stochastic differential equations with multiplicative noise. Therefore, they have to be interpreted as Stratonovich-Langevin equations and the roles of stochastic calculus have to be used in the simulations. In our simulations, the response functions are "measured" and from them the complex susceptibilities are calculated. We performed several simulations, varying each parameter around a standard value, in order to see how the susceptibilities are correlated with the physical constants of the material. In the conclusions of special mention is the verification that the line broadening is very big. To be explicit, the ratio of the line-width of the polydisperse to that of the monodisperse with a diameter equal to the median diameter of the polydisperse, is much bigger than the ratio of the diameter's distribution width to the median diameter. It is interesting to note that for small dispersion width of diameters the resonance frequency does not change significantly with respect to the resonance frequency of the monodisperse. Figs 7, Refs 6.

Scherer, C.

2007-12-01

368

Stretching of a confined ferrofluid: Influence of viscous stresses and magnetic field

NASA Astrophysics Data System (ADS)

An analytical investigation is presented for the stretch flow of a viscous Newtonian ferrofluid highly confined between parallel plates. We focus on the development of interfacial instabilities when the upper plate is lifted at a described rate, under the action of an applied magnetic field. We derive the mode-coupling differential equation for the interface perturbation amplitudes and study both linear and nonlinear flow regimes. In contrast to the great majority of works in stretch flow we take into account stresses originated from velocity gradients normal to the ferrofluid interface. The impact of such normal stresses is accounted for through a modified Young-Laplace pressure jump interfacial boundary condition, which also includes the contribution from magnetic normal traction. We study how the stability properties of the interface and the shape of the emerging patterns respond to the combined action of normal stresses and magnetic field, both in the presence and absence of surface tension. We show that the inclusion of normal viscous stresses introduces a pertinent dependence on the initial aspect ratio, indicating that the number of fingers formed would be overestimated if such stresses are not taken into account. At early linear stages it is found that such stresses regularize the system, acting as an effective interfacial tension. At weakly nonlinear stages we verified that normal stresses reduce finger competition, which can be completely suppressed with the assistance of an azimuthal magnetic field. We have also found that the magnetic normal traction introduces a purely nonlinear contribution to the problem, revealing the key role played by the magnetic susceptibility in the control of finger competition.

Oliveira, Rafael M.; Miranda, José A.

2006-03-01

369

Load responsive hydrodynamic bearing

A load responsive hydrodynamic bearing is provided in the form of a thrust bearing or journal bearing for supporting, guiding and lubricating a relatively rotatable member to minimize wear thereof responsive to relative rotation under severe load. In the space between spaced relatively rotatable members and in the presence of a liquid or grease lubricant, one or more continuous ring shaped integral generally circular bearing bodies each define at least one dynamic surface and a plurality of support regions. Each of the support regions defines a static surface which is oriented in generally opposed relation with the dynamic surface for contact with one of the relatively rotatable members. A plurality of flexing regions are defined by the generally circular body of the bearing and are integral with and located between adjacent support regions. Each of the flexing regions has a first beam-like element being connected by an integral flexible hinge with one of the support regions and a second beam-like element having an integral flexible hinge connection with an adjacent support region. A least one local weakening geometry of the flexing region is located intermediate the first and second beam-like elements. In response to application of load from one of the relatively rotatable elements to the bearing, the beam-like elements and the local weakening geometry become flexed, causing the dynamic surface to deform and establish a hydrodynamic geometry for wedging lubricant into the dynamic interface.

Kalsi, Manmohan S. (Houston, TX); Somogyi, Dezso (Sugar Land, TX); Dietle, Lannie L. (Stafford, TX)

2002-01-01

370

Field-induced structure formation in a ferrofluid with well-defined magnetite nanoparticles with a permanent magnetic dipole moment was studied with small-angle neutron scattering (SANS) as a function of the magnetic interactions. The interactions were tuned by adjusting the size of the well-defined, single-magnetic-domain magnetite (Fe{sub 3}O{sub 4}) particles and by applying an external magnetic field. For decreasing particle dipole moments, the data show a progressive distortion of the hexagonal symmetry, resulting from the formation of magnetic sheets. The SANS data show qualitative agreement with recent cryogenic transmission electron microscopy results obtained in 2D [Klokkenburg et al., Phys. Rev. Lett. 97, 185702 (2006)] on the same ferrofluids.

Klokkenburg, M.; Erne, B. H.; Petukhov, A. V.; Philipse, A. P. [Van 't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute, Utrecht University, Padualaan 8, 3584 CH Utrecht (Netherlands); Wiedenmann, A. [Hahn-Meitner-Institut Berlin, Department SF3, Glienickerstrasse 100, D-14109 Berlin (Germany)

2007-05-15

371

With this work we would like to emphasize the necessity of steric repulsion to stabilize novel ionic liquid-based ferrofluids. For this purpose, we prepared a suspension of magnetite nanoparticles coated with a double layer of oleic acid, dispersed in 1-ethyl-3-methylimidazolium ethylsulphate ([EMIM][EtSO(4)]). For comparison, a suspension of bare magnetite nanoparticles in [EMIM][EtSO(4)] was also prepared. The stability of these suspensions was checked by magnetic sedimentation and centrifugation processes. Furthermore, their yield stress was measured as a function of the applied magnetic field, which gave additional information on their stability. The results of these experiments showed that the suspension of bare nanoparticles was rather unstable, whereas the suspension of double layer coated nanoparticles gave rise to a true (stable) ferrofluid. PMID:21345446

Rodríguez-Arco, Laura; López-López, Modesto T; González-Caballero, Fernando; Durán, Juan D G

2011-05-01

372

Synthesis and characterization of iron-rich FexPt1-x ferrofluid for magnetic resonance imaging

NASA Astrophysics Data System (ADS)

Iron-rich FexPt1-x ultrafine nanodots were prepared by a simple and versatile polyol process using a combinatorial strategy of introducing a strong reducing agent and decreasing the synthesis temperature. The native hydrophobic nanodots were converted into a wettable dispersion by ligand exchange-mediated phase transformation using tetramethyl ammonium hydroxide. The microstructural study confirmed the formation of Fe-rich FePt nanodots having an average particle size of ~3.5 nm with a narrow size distribution. An MTT (methylthiazolyldiphenyl-tetrazolium bromide [3- (4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide]) study on mammalian leukocyte cultures confirmed the high degree of biocompatibility for the ferrofluid. The ferrofluid, when studied for its concentration-dependent transverse relaxation time and contrast properties, was found to exhibit promising properties as a magnetic resonance imaging T2 contrast agent.

Jha, Deepak K.; Deb, P.; Kalita, E.; Shameem, M.; Patel, Anant B.

2012-03-01

373

NASA Astrophysics Data System (ADS)

Evidence is presented from studies of electron magnetic resonance for the formation of linear chains in kerosene based Mn 0.1Fe 0.9Fe 2O 4 (MF1) ferrite ferrofluid cooled in a magnetic field. The resonance field at 77 K was found to depend on the field at which the sample was cooled. More interestingly, the samples cooled in a magnetic field exhibited anisotropy in a resonance field with 180° periodicity, giving evidence for frozen chains.

Sastry, M. D.; Babu, Y.; Goyal, P. S.; Mehta, R. V.; Upadhyay, R. V.; Srinivas, D.

1995-08-01

374

Microscopic models of hydrodynamic behavior

We review recent developments in the rigorous derivation of hydrodynamic-type macroscopic equations from simple microscopic models: continuous time stochastic cellular automata. The deterministic evolution of hydrodynamic variables emerges as the “law of large numbers,” which holds with probability one in the limit in which the ratio of the microscopic to the macroscopic spatial and temporal scales go to zero. We

Joel L. Lebowitz; Errico Presutti; Herbert Spohn

1988-01-01

375

An HLLC Riemann solver for magneto-hydrodynamics

NASA Astrophysics Data System (ADS)

This paper extends a class of approximate Riemann solvers devised by Harten, Lax and van Leer (HLL) for Euler equations of hydrodynamics to magneto-hydrodynamics (MHD) equations. In particular, we extend the two-state HLLC (HLL for contact wave) construction of Toro, Spruce and Speares to MHD equations. We derive a set of HLLC middle states that satisfies the conservation laws. Numerical examples are given to demonstrate that the new MHD-HLLC solver can achieve high numerical resolution, especially for resolving contact discontinuity. In addition, this new solver maintains a high computational efficiency when compared to Roe's approximate Riemann solver.

Li, Shengtai

2005-02-01

376

Central Amazon Floodplain Hydrodynamics

NASA Astrophysics Data System (ADS)

Amazon floodplain wetlands contain high biological diversity for which the flow regime, particularly the flood-pulse, provides the driving force. Surface water flow is recognized as the key factor in the establishment and maintenance of wetland ecosystems and their functioning, exerting a strong control on channel formation and determining the spatial and temporal complexity of wetland habitats. However, the hydrodynamics of seasonally flooded wetlands in the Amazon basin remains poorly quantified through ground observations, satellite observations or modelling. In this research, fieldwork was conducted between March and August 2012 for 850 km^{2} of várzea floodplain to the south of a 75 km reach of the Rio Solimões, downstream (east) of the confluence with the Rio Purus. The primary aim of this was to collect ground-based measurements of surface water flows from mid-rising, through high-water to mid-falling flood conditions to allow a detailed picture of floodplain hydrodynamics to be constructed. Four 10-day periods of fieldwork were completed, during which measurements were taken at 42 locations along the floodplain channel network and in floodplain lakes, together with main channel measurements on the Solimões and Purus. Measurements were obtained of: (i) flow rates along floodplain channels, using an Acoustic Current Doppler Profiler (ADCP); (ii) runoff from terra firma via measurement of flows out of ria lakes at the southern edge of the floodplain; (iii) water conductivity; and (iv) suspended sediment concentrations. Overbank flow rates from the Rio Solimões and Rio Purus into the floodplain forest were also obtained using a current meter at several locations during high water. In addition, floodplain channel and lake depths were obtained using continuous recording of sonar connected to a Global Positioning System, enabling the estimation of bathymetry. Using these measurements, detailed hydrodynamic maps of the floodplain were produced from mid-rising to mid-falling flood stages. Initial results show that floodplain channels play an important role in floodplain hydrodynamics, carrying the bulk of flood water into the floodplain during rising water. Once main-channel water levels are above-bankfull, overbank flow directly into the floodplain forest becomes significant. At high-water, the flow rate out of the Purus along the major floodplain channel was 2,200 m^{3}s^{-1}, representing around 10% of the total Purus channel flow ( 23,000 m^{3}s^{-1} at Beruri). In addition, an estimated 2,000 - 4,000 m^{3}s^{-1} of overbank flow occurred from the lower Purus into the floodplain. Floodplain channel flow from the Solimões was less significant than from the Purus at less than 1,000 m^{3}s^{-1}, under 1% of Solimões channel flow ( 116,000 m^{3}s^{-1} upstream of the Purus); however overbank flow into the floodplain forest may have been as much as 10,000 m^{3}s^{-1} along the study reach. Terra firma runoff, measured at the outflows of ria lakes, contributed an insignificant amount of flow during the measurement periods. The first-order estimate of flow through the floodplain area during high water was 15,000 to 17,000 m^{3}s^{-1} (an average of 17.6 to 20.0 m^{3}s^{-1} per km^{2}), with 30-40% of the flow contributed by the Purus.

Wilson, M. D.; Vega, M. C.; Forsberg, B. R.

2012-12-01

377

Hydrodynamic effects on coalescence.

The goal of this project was to design, build and test novel diagnostics to probe the effect of hydrodynamic forces on coalescence dynamics. Our investigation focused on how a drop coalesces onto a flat surface which is analogous to two drops coalescing, but more amenable to precise experimental measurements. We designed and built a flow cell to create an axisymmetric compression flow which brings a drop onto a flat surface. A computer-controlled system manipulates the flow to steer the drop and maintain a symmetric flow. Particle image velocimetry was performed to confirm that the control system was delivering a well conditioned flow. To examine the dynamics of the coalescence, we implemented an interferometry capability to measure the drainage of the thin film between the drop and the surface during the coalescence process. A semi-automated analysis routine was developed which converts the dynamic interferogram series into drop shape evolution data.

Dimiduk, Thomas G.; Bourdon, Christopher Jay; Grillet, Anne Mary; Baer, Thomas A.; de Boer, Maarten Pieter; Loewenberg, Michael (Yale University, New Haven, CT); Gorby, Allen D.; Brooks, Carlton, F.

2006-10-01

378

Air–water two-phase flow modeling of turbulent surf and swash zone wave motions

Wave breaking and wave runup\\/rundown have a major influence on nearshore hydrodynamics, morphodynamics and beach evolution. In the case of wave breaking, there is significant mixing of air and water at the wave crest, along with relatively high kinetic energy, so prediction of the free surface is complicated. Most hydrodynamic studies of surf and swash zone are derived from single-phase

R. Bakhtyar; A. M. Razmi; D. A. Barry; A. Yeganeh-Bakhtiary; Q.-P. Zou

379

NASA Technical Reports Server (NTRS)

An electromechanical actuator for producing mechanical force and/or motion in response to electrical signals is disclosed. The actuator includes a ferromagnetic fluid and a coil which are contained within an elastomeric capsule. Energization of the coil by application of current to a pair of coil electrodes extending through the walls of the elastomeric capsule produces distortion of the capsule, i.e., radial expansion and axial contraction. This distortion is caused by the redistribution of the ferromagnetic fluid within the capsule under the influence of the magnetic field. Variation of the current input will produce corresponding variations in the degree of capsule distortion.

Sabelman, E. E. (inventor)

1973-01-01

380

Evaluation of using ferrofluid as an interface material for a field-reversible thermal connector

NASA Astrophysics Data System (ADS)

The electrical functionality of an avionics chassis is limited due to heat dissipation limits. The limits arise due to the fact that components in an avionic computer boxes are packed very compactly, with the components mounted onto plug-in cards, and the harsh environment experienced by the chassis limits how heat can be dissipated from the cards. Convective and radiative heat transfer to the ambient are generally not possible. Therefore it is necessary to have heat transferred from the components conducted to the edge of the plug-in cards. The heat then needs to conduct from the card edge to a cold block that not only holds the card in place, but also removes the generated heat by some heat transfer fluid that is circulated through the cold block. The interface between the plug-in card and the cold block typically has a high thermal resistance since it is necessary for the card to have the capability to be re-workable, meaning that the card can be removed and then returned to the chassis. Reducing the thermal resistance of the interface is the objective of the current study and the topic of this thesis. The current design uses a pressure interface between the card and cold block. The contact pressure is increased through the addition of a wedgelock, which is a field-reversible mechanical connector. To use a wedgelock, the cold block has channels milled on the surface with widths that are larger than the thickness of the plug-in card and the un-expanded wedgelock. The card edge is placed in the channel and placed against one of the channel walls. A wedgelock is then placed between the card and the other channel wall. The wedgelock is then expanded by using either a screw or a lever. As the wedgelock expands it fills in the remaining channel gap and bears against the other face of the plug-in card. The majority of heat generated by the components on the plug-in card is forced to conduct from the card into the wall of the cold block, effectively a single sided, dry conduction heat transfer path. Having started as a student design competition named RevCon Challenge, work was performed to evaluate the use of new field-reversible thermal connectors. The new design proposed by the University of Missouri utilized oil based iron nanoparticles, commonly known as a ferrofluid, as a thermal interface material. By using a liquid type of interface material the channel gap can be reduced to a few micrometers, within machining tolerances, and heat can be dissipated off both sides of the card. The addition of nanoparticles improves the effective thermal conductivity of base fluid. The use of iron nanoparticles allows magnets to be used to hold the fluid in place, so the electronic cards may be easily inserted and removed while keeping the ferrofluid in the cold block channel. The ferrofluid-based design which was investigated has shown lower thermal resistance than the current wedgelock design. These results open the door for further development of electronic cards by using higher heat emitting components without compromising the simplicity of attaching/detaching cards from cooling plates.

Yousif, Ahmed S.

381

Constraining relativistic viscous hydrodynamical evolution

We show that by requiring positivity of the longitudinal pressure it is possible to constrain the initial conditions one can use in second-order viscous hydrodynamical simulations of ultrarelativistic heavy-ion collisions. We demonstrate this explicitly for (0+1)-dimensional viscous hydrodynamics and discuss how the constraint extends to higher dimensions. Additionally, we present an analytic approximation to the solution of (0+1)-dimensional second-order viscous hydrodynamical evolution equations appropriate to describe the evolution of matter in an ultrarelativistic heavy-ion collision.

Martinez, Mauricio [Helmholtz Research School and Otto Stern School, Goethe-Universitaet Frankfurt am Main Ruth-Moufang-Strasse 1, D-60438 Frankfurt am Main (Germany); Strickland, Michael [Physics Department, Gettysburg College Gettysburg, Pennsylvania 17325 (United States)

2009-04-15

382

Anisotropic hydrodynamics: Motivation and methodology

NASA Astrophysics Data System (ADS)

In this proceedings contribution I review recent progress in our understanding of the bulk dynamics of relativistic systems that possess potentially large local rest frame momentum-space anisotropies. In order to deal with these momentum-space anisotropies, a reorganization of relativistic viscous hydrodynamics can be made around an anisotropic background, and the resulting dynamical framework has been dubbed "anisotropic hydrodynamics". I also discuss expectations for the degree of momentum-space anisotropy of the quark-gluon plasma generated in relativistic heavy ion collisions at RHIC and LHC from second-order viscous hydrodynamics, strong-coupling approaches, and weak-coupling approaches.

Strickland, Michael

2014-06-01

383

NASA Astrophysics Data System (ADS)

Microfluidic networks and microporous materials have long been of interest in areas such as hydrology, petroleum engineering, chemical and electrochemical engineering, medicine and biochemical engineering. With the emergence of new processes in gas separation, cell sorting, ultrafiltration, and advanced materials synthesis, the importance of building a better qualitative and quantitative understanding of these key technologies has become apparent. However, microfluidic measurement and theory is still relatively underdeveloped, presenting a significant obstacle to the systematic design of microfluidic devices and materials. Theoretical challenges arise from the breakdown of classical viscous flow models as the flow dimensions approach the mean free path of individual molecules. Experimental challenges arise from the lack of flow profilometry techniques at sub-micron length scales. Here we present an extension of scanning probe microscopy techniques, which we have termed Hydrodynamic Force Microscopy (HFM). HFM exploits fluid drag to profile microflows and to map the permeability of microporous materials. In this technique, an atomic force microscope (AFM) cantilever is scanned close to a microporous sample surface. The hydrodynamic interactions arising from a pressure-driven flow through the sample are then detected by mapping the deflection of an AFM cantilever. For gas flows at atmospheric pressure, HFM has been shown to achieve a velocity sensitivity of 1 cm/s with a spatial resolution of ˜ 10 nm. This compares very favorably to established techniques such as hot-wire and laser Doppler anemometry, whose spatial resolutions typically exceed 1 mum and which may rely on the use of tracer particles or flow markers1. We demonstrate that HFM can successfully profile Poiseuille flows inside pores as small as 100 nm and can distinguish Poiseuille flow from uniform flow for short entry lengths. HFM detection of fluid jets escaping from porous samples can also reveal a "permeability map" of a sample's pore structure, allowing us to distinguish between clear and blocked pores, even in cases where the subsurface fouling is undetectable by conventional AFM. The experimental data is discussed in context with theoretical aspects of HFM microflow measurement and practical limits of this technique. Finally, we conclude with variations of standard HFM techniques that show some promise for investigation of smaller nanometer-scale flows of gases and liquids.

Ulrich, Elaine Schmid

384

NASA Astrophysics Data System (ADS)

Ferrofluids are colloidal systems composed of a single domain of magnetic nanoparticles with a mean diameter around 30 nm, dispersed in a liquid carrier. Magnetic Co (1- x) Zn xFe 2O 4 ( x=0.25, 0.50, 0.75) ferrite nanoparticles were prepared via co-precipitation method from aqueous salt solutions in an alkaline medium. The composition and structure of the samples were characterized through Energy Dispersive X-ray Spectroscopy and X-ray diffraction, respectively. Transmission Electron Microscopy (TEM) studies permitted determining nanoparticle size; grain size of nanoparticle conglomerates was established via Atomic Force Microscopy. The magnetic behavior of ferrofluids was characterized by Vibrating Sample Magnetometer (VSM); and finally, a magnetic force microscope was used to visualize the magnetic domains of Co (1- x) Zn xFe 2O 4 nanoparticles. X-ray diffraction patterns of Co (1- x) Zn xFe 2O 4 show the presence of the most intense peak corresponding to the (311) crystallographic orientation of the spinel phase of CoFe 2O 4. Fourier Transform Infrared Spectroscopy confirmed the presence of the bonds associated to the spinel structures; particularly for ferrites. The mean size of the crystallite of nanoparticles determined from the full-width at half maximum of the strongest reflection of the (311) peak by using the Scherrer approximation diminished from (9.5±0.3) nm to (5.4±0.2) nm when the Zn concentration increases from 0.21 to 0.75. The size of the Co-Zn ferrite nanoparticles obtained by TEM is in good agreement with the crystallite size calculated from X-ray diffraction patterns, using Scherer's formula. The magnetic properties investigated with the aid of a VSM at room temperature presented super-paramagnetic behavior, determined by the shape of the hysteresis loop. In this study, we established that the coercive field of Co (1- x) Zn xFe 2O 4 magnetic nanoparticles, the crystal and nanoparticle sizes determined by X-ray Diffraction and TEM, respectively, decrease with the increase of the Zn at%. Finally, our magnetic nanoparticles are not very hard magnetic materials given that the hysteresis loop is small and for this reason Co (1- x) Zn xFe 2O 4 nanoparticles are considered as soft magnetic material.

López, J.; González-Bahamón, L. F.; Prado, J.; Caicedo, J. C.; Zambrano, G.; Gómez, M. E.; Esteve, J.; Prieto, P.

2012-02-01

385

Estimation of Internal Wave Currents from Sar and Infrared Scatterometer Imagery.

National Technical Information Service (NTIS)

Models for estimating internal-wave surface currents from SAR and infrared scatterometer images of the ocean surface are presented. Selected SAR images were analyzed using linear hydrodynamic interaction theory and first-order hydrodynamic interaction the...

S. J. Hughes B. A. Hughes

1986-01-01

386

Basics of smoothed particle hydrodynamics.

National Technical Information Service (NTIS)

We present a review of the smoothed particle hydrodynamics (SPH) method and present several sample problems to illustrate its properties as a general purpose computational fluid dynamics technique. Accuracy and efficiency are also assessed. Our findings s...

L. D. Cloutman

1990-01-01

387

Analysis of smoothed particle hydrodynamics.

National Technical Information Service (NTIS)

SPH (Smoothed Particle Hydrodynamics) is a gridless Lagrangian technique which is appealing as a possible alternative to numerical techniques currently used to analyze high deformation impulsive loading events. In the present study, the SPH algorithm has ...

J. W. Swegle S. W. Attaway M. W. Heinstein F. J. Mello D. L. Hicks

1994-01-01

388

Inducer Hydrodynamic Load Measurement Devices.

National Technical Information Service (NTIS)

Marshall Space Flight Center (MSFC) has demonstrated two measurement devices for sensing and resolving the hydrodynamic loads on fluid machinery. The first - a derivative of the six-component wind tunnel balance - senses the forces and moments on the rota...

S. E. Skelley T. F. Zoladz

2002-01-01

389

Hydrodynamic instabilities in inertial fusion.

National Technical Information Service (NTIS)

This report discusses topics on hydrodynamics instabilities in inertial confinement: linear analysis of Rayleigh-Taylor instability; ablation-surface instability; bubble rise in late-stage Rayleigh-Taylor instability; and saturation and multimode interact...

N. M. Hoffman

1994-01-01

390

Hydrodynamic synchronization of colloidal oscillators

Two colloidal spheres are maintained in oscillation by switching the position of an optical trap when a sphere reaches a limit position, leading to oscillations that are bounded in amplitude but free in phase and period. The interaction between the oscillators is only through the hydrodynamic flow induced by their motion. We prove that in the absence of stochastic noise the antiphase dynamical state is stable, and we show how the period depends on coupling strength. Both features are observed experimentally. As the natural frequencies of the oscillators are made progressively different, the coordination is quickly lost. These results help one to understand the origin of hydrodynamic synchronization and how the dynamics can be tuned. Cilia and flagella are biological systems coupled hydrodynamically, exhibiting dramatic collective motions. We propose that weakly correlated phase fluctuations, with one of the oscillators typically precessing the other, are characteristic of hydrodynamically coupled systems in the presence of thermal noise.

Kotar, Jurij; Leoni, Marco; Bassetti, Bruno; Lagomarsino, Marco Cosentino; Cicuta, Pietro

2010-01-01

391

The two-dimensional radiation-hydrodynamic code SN-YAQUI was used to calculate the evolution of a hypothetical nuclear fireball of 1-Mt yield at a burst altitude of 500 m. The ground-reflected shock wave interacts strongly with the fireball and induces the early formation of a rapidly rotating ring-shaped vortex. The hydrodynamic and radiation phenomena are discussed.

Horak, H.G.; Jones, E.M.; Sandford, M.T. II; Whitaker, R.W.; Anderson, R.C.; Kodis, J.W.

1982-03-01

392

Geodesics of Sound Waves and Their Wave Fronts in Curved Space-Time

In order to clarify the focusing effects of the energy and momentum by wave motion, the wave propagations of a photon and sound wave are investigated in Kerr space-time. By using a canonical-type formulation for the propagations of electromagnetic disturbances in vacuum and hydrodynamical disturbances in accretion disk, the basic properties of sound wave propagation and the numerical calculations of

Masaaki Takahashi; Toshihisa Ishizuka; Masayoshi Yokosawa

1990-01-01

393

On the anomalous superfluid hydrodynamics

It has been shown by Son and Surówka that the presence of anomaly in hydrodynamics with global U(1) symmetry can induce vortical and magnetic currents. The induced current is uniquely determined by anomaly from the existence of an entropy current with non-negative divergence. In this work, we extended the analysis to hydrodynamics with U(1) symmetry spontaneously broken, i.e. U(1) superfluid

Shu Lin

2011-01-01

394

Generation and Propagation of Nonlinear Waves in Travelling Wave Tubes

The generation and evolution of nonlinear waves in microwave amplifiers such as travelling wave tubes, free electron lasers and klystrons have been studied. The analysis is based on the hydrodynamic and field equations for the self-consistent evolution of the beam density distribution, the current velocity and the electromagnetic fields. A system of coupled nonlinear Schr\\\\\\

Stephan I. Tzenov; E. R. Caianiello

2005-01-01

395

NASA Astrophysics Data System (ADS)

We report on the observation of all-optically tunable Goos-Hänchen (GH) shift in a symmetrical metal-cladding waveguide, whose guiding layer is filled with the water-based ferrofluid. The strong dependence of the GH shift and its switching time on the control beam power is suggested to be arising from the light-induced periodic-like microstructure transitions of ferrofluid in virtue of the competition between the optical trapping effect and the Soret effect. The indirect evidence of our qualitative hypothesis is given. The presented tunability of GH shift may have potential applications in optical switching and sensing.

Wang, Xianping; Yin, Cheng; Sun, Jingjing; Li, Honggen; Sang, Minghuang; Yuan, Wen; Cao, Zhuangqi; Huang, Meizhen

2013-10-01

396

Ferrofluid pipe flow under the influence of the magnetic field of a cylindrical coil

NASA Astrophysics Data System (ADS)

Ferrofluid pipe flow under the effect of a co-linear, finite length cylindrical coil is examined numerically. The specific flow configuration is chosen as it is encountered in engineering and bioengineering applications such as magnetic drug targeting systems. The objective of the paper is twofold: first, to investigate the accuracy of an analytical solution for the magnetization equation and assess its validity when used for non-uniform magnetic fields. It is found that it can be very helpful as a means of estimating the magnetization, especially for strong magnetic fields with low gradients; second, to examine the effects of the magnetic field on the flow and study the relevant importance of the magnetic terms of the momentum equation. The parameters that we examine are the strength of the magnetic field and of its gradients, the volumetric concentration of the magnetic particles, and the dimensions (length and diameter) of the coil. It is revealed that the axial pressure drop depends linearly on the volumetric concentration and that the magnetoviscosity effect is negligible in cases of non-uniform magnetic fields.

Papadopoulos, P. K.; Vafeas, P.; Hatzikonstantinou, P. M.

2012-12-01

397

Analytical centrifugation is used for the first time to measure sedimentation equilibrium concentration profiles of a ferrofluid, a concentrated colloidal dispersion of strongly absorbing magnetic nanoparticles. To keep the optical absorbance from becoming too strong, the optical path length is restricted to 50 ?m by placing the dispersion in a flat glass capillary. The concentration profile is kept from becoming too steep, despite the relatively high buoyant mass of the nanoparticles, by making novel use of a low-velocity analytical centrifuge that was not designed to measure equilibrium profiles. The experimental approach is validated by comparison with profiles obtained using an analytical ultracentrifuge. At concentrations of a few hundred grams per liter, the osmotic pressures calculated from the equilibrium profiles are lower than expected for hard spheres or non-interacting particles, due to magnetic dipolar interactions. By following the presented experimental approach, it will now also be possible to characterize the interparticle interactions of other strongly absorbing colloidal particles not studied before by analytical centrifugation. PMID:22617483

Luigjes, Bob; Thies-Weesie, Dominique M E; Philipse, Albert P; Erné, Ben H

2012-06-20

398

The formation of spherical superparamagnetic colloidal aggregates of magnetite nanoparticles by emulsification of a ferrofluid and subsequent solvent evaporation has been systematically studied. The colloidal aggregates occur as a dense sphere with magnetite nanoparticles randomly packed and preserved particle-particle separation due to chemisorbed oleic acid. The voids between nanoparticles are filled with solvent and free oleic acid. The latter was found to influence the formation of colloidal aggregates and their surface properties. The choice of surfactant, whether low molecular weight or polymeric, was shown to lead to the colloidal aggregates having tailored interfacial behavior. Magnetization measurements at ambient temperature revealed that the magnetite colloidal aggregates preserve the superparamagnetic properties of the starting nanoparticle units and show high saturation magnetization values up to 57 emu/g. The size distribution of magnetite nanoparticle colloidal aggregates produced by such an approach was found to be a function of emulsion droplet breakup-coalescence and stabilization kinetics and therefore is influenced by the emulsification process conditions and concentrations of the emulsion compounds. PMID:22365838

Lobaz, Volodymyr; Klupp Taylor, Robin N; Peukert, Wolfgang

2012-05-15

399

NASA Astrophysics Data System (ADS)

An established biomimetic process for the synthesis of aqueous ferrofluids using polymers has been subjected to systematic microwave irradiation at different wattages primarily to see if the magnetization could be increased by microwave irradiation and if so how would it affect the stability of the fluid. Care has been taken to maintain ambient conditions of synthesis even after three cycles of microwave irradiation before oxidation and ten cycles after it, so as not to violate the basic principles of the process. Detailed characterization using, x-ray diffractometry, transmission electron microscopy, fourier transform infra-red spectroscopy, dynamic light scattering, thermo-gravimetric analysis, differential thermal analysis and vibrating sample magnetometry showed that these fluids containing iron oxide nanoparticles-poly(vinyl) alcohol nanocomposites are highly stable in the proportions established by us. Measurements at five different wattages double the saturation magnetization but the stability remains unaffected compared to the one without microwave irradiation, forcing us to believe that the incubation of the iron salt solution and the polymer in the right proportion before oxidation is what contributes to the stability and that increasing the number of cycles of microwave irradiation at this stage, perhaps, would have led to a more pronounced effect.

Bhattacharya, Soumya; Jenamoni, Krishna; Nayar, Suprabha

2012-10-01

400

The Use of Ferrofluids to Model Materials Processing (MSFC Center Director's Discretionary Fund)

NASA Technical Reports Server (NTRS)

Many crystals grown in space have structural flaws believed to result from convective motions during the growth phase. The character of these instabilities is not well understood but is associated with thermal and solutal density variations near the solidification interface in the presence of residual gravity and g-jitter. To study these instabilities in a separate, controlled space experiment, a concentration gradient would first have to be artificially established in a timely manner as an initial condition. This is generally difficult to accomplish in a microgravity environment because the momentum of the fluid injected into a test cell tends to swirl around and mix in the absence of a restoring force. The use of magnetic fields to control the motion and position of liquids has received recent, growing interest. The possibility of using the force exerted by a non-uniform magnetic field on a ferrofluid to not only achieve fluid manipulation but also to actively control fluid motion makes it an attractive candidate for space applications. This paper describes a technique for quickly establishing a linear or exponential fluid concentration gradient using a magnetic field in place of gravity to stabilize the deployment. Also discussed is a photometric technique for measuring the concentration profile using light attenuation. Although any range of concentrations can be realized, photometric constraints impose some limitations on measurements. Results of the ground-based experiments indicate that the species distribution is within 3 percent of the predicted value.

Leslie, F.; Ramachandran, N.

2000-01-01

401

Hydrodynamic modes in a confined granular fluid.

Confined granular fluids, placed in a shallow box that is vibrated vertically, can achieve homogeneous stationary states due to energy injection mechanisms that take place throughout the system. These states can be stable even at high densities and inelasticities allowing for a detailed analysis of the hydrodynamic modes that govern the dynamics of granular fluids. By analyzing the decay of the time correlation functions it is shown that there is a crossover from a quasielastic regime in which energy evolves as a slow mode to an inelastic regime with energy slaved to the other conserved fields. The two regimes have well differentiated transport properties and in the inelastic regime the dynamics can be described by a reduced hydrodynamics with modified longitudinal viscosity and sound speed. The crossover between the two regimes takes place at a wave vector that is proportional to the inelasticity. A two-dimensional granular model, with collisions that mimic the energy transfers that take place in a confined system, is studied by means of microscopic simulations. The results show excellent agreement with the theoretical framework and allow validation of hydrodynamiclike models. PMID:23496507

Brito, Ricardo; Risso, Dino; Soto, Rodrigo

2013-02-01

402

Quantum hydrodynamics: capturing a reactive scattering resonance.

The hydrodynamic equations of motion associated with the de Broglie-Bohm formulation of quantum mechanics are solved using a meshless method based upon a moving least-squares approach. An arbitrary Lagrangian-Eulerian frame of reference and a regridding algorithm which adds and deletes computational points are used to maintain a uniform and nearly constant interparticle spacing. The methodology also uses averaged fields to maintain unitary time evolution. The numerical instabilities associated with the formation of nodes in the reflected portion of the wave packet are avoided by adding artificial viscosity to the equations of motion. A new and more robust artificial viscosity algorithm is presented which gives accurate scattering results and is capable of capturing quantum resonances. The methodology is applied to a one-dimensional model chemical reaction that is known to exhibit a quantum resonance. The correlation function approach is used to compute the reactive scattering matrix, reaction probability, and time delay as a function of energy. Excellent agreement is obtained between the scattering results based upon the quantum hydrodynamic approach and those based upon standard quantum mechanics. This is the first clear demonstration of the ability of moving grid approaches to accurately and robustly reproduce resonance structures in a scattering system. PMID:16108631

Derrickson, Sean W; Bittner, Eric R; Kendrick, Brian K

2005-08-01

403

Hydrodynamic regime of two-dimensional electron magnetohydrodynamics

A detailed numerical simulation studying certain aspects of turbulence in the electron magnetohydrodynamic (EMHD) model is presented. In particular, new studies have been carried out in a parameter regime where the typical turbulent length scales are comparable to or smaller than the electron skin depth. This is the regime where the EMHD turbulence has similar traits to the hydrodynamic turbulence and the wave propagation effects due to whistlers are believed to be inconsequential. (c) 2000 American Institute of Physics.

Dastgeer, Sheikh [Institute For Plasma Research, Bhat, Gandhinagar, 382428, (India)] [Institute For Plasma Research, Bhat, Gandhinagar, 382428, (India); Das, Amita [University of California, San Diego, La Jolla, California 92093 (United States)] [University of California, San Diego, La Jolla, California 92093 (United States); Kaw, Predhiman [Institute For Plasma Research, Bhat, Gandhinagar, 382428, (India)] [Institute For Plasma Research, Bhat, Gandhinagar, 382428, (India)

2000-05-01

404

Hydrodynamic aspects of caldera-forming eruptions: Numerical models

Compariosn of results from a two-dimensional numerical eruption simulation (KACHINA) to calculations based upon a shock tube analog supports the conclusion that the hydrodynamics during the initial minutes of large caldrs-forming ash flow ruptions may be dominated by blast wave phenomena. Field evidence for this phenomonology is pyroclastic surge deposits commonly occurring both directly below caldera-related ash flow sheets, on

K. H. Wohletz; T. R. McGetchin; M. T. Sandford II; E. M. Jones

1984-01-01

405

Film rupture in the diffuse interface model coupled to hydrodynamics

The process of dewetting of a thin liquid film is usually described using a long-wave approximation yielding a single evolution equation for the film thickness. This equation incorporates an additional pressure term-the disjoining pressure-accounting for the molecular forces. Recently a disjoining pressure was derived coupling hydrodynamics to the diffuse interface model [L. M. Pismen and Y. Pomeau, Phys. Rev. E

Uwe Thiele; Manuel G. Velarde; Kai Neuffer; Yves Pomeau

2001-01-01

406

A new hydrodynamic analysis of double layers

NASA Technical Reports Server (NTRS)

A genuine two-fluid model of plasmas with collisions permits the calculation of dynamic (not necessarily static) electric fields and double layers inside of plasmas including oscillations and damping. For the first time a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser-produced plasmas showing very high dynamic electric fields in nonlinear force-produced cavitous and inverted double layers in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. Results are the rotation of plasmas in magnetic fields and a new second harmonic resonance, explanation of the measured inverted double layers, explanation of the observed density-independent, second harmonics emission from laser-produced plasmas, and a laser acceleration scheme by the very high fields of the double layers.

Hora, Heinrich

1987-01-01

407

National Technical Information Service (NTIS)

A method for calculating the energy take-out from a single wave energy converter is presented. The converter consists of a buoy connected via a hose pump to a submerged plate. The equations of motion of the buoy and plate are solved linearly in the freque...

L. Berggren

1992-01-01

408

Hydrodynamics of coalescing binary neutron stars: Ellipsoidal treatment

NASA Technical Reports Server (NTRS)

We employ an approximate treatment of dissipative hydrodynamics in three dimensions to study the coalescence of binary neutron stars driven by the emission of gravitational waves. The stars are modeled as compressible ellipsoids obeying a polytropic equation of state; all internal fluid velocities are assumed to be linear functions of the coordinates. The hydrodynamics equations then reduce to a set of coupled ordinary differential equations for the evolution of the principal axes of the ellipsoids, the internal velocity parameters, and the binary orbital parameters. Gravitational radiation reaction and viscous dissipation are both incorporated. We set up exact initial binary equilibrium configurations and follow the transition from the quasi-static, secular decay of the orbit at large separation to the rapid dynamical evolution of the configurations just prior to contact. A hydrodynamical instability resulting from tidal interactions significantly accelerates the coalescence at small separation, leading to appreciable radial infall velocity and tidal lag angles near contact. This behavior is reflected in the gravitational waveforms and may be observable by gravitational wave detectors under construction. In cases where the neutron stars have spins which are not aligned with the orbital angular momentum, the spin-induced quadrupole moment can lead to precession of the orbital plane and therefore modulation of the gravitational wave amplitude even at large orbital radius. However, the amplitude of the modulation is small for typical neutron star binaries with spins much smaller than the orbital angular momentum.

Lai, Dong; Shapiro, Stuart L.

1995-01-01

409

Application of Multi-block Grid and Parallelization Techniques in Hydrodynamic Modelling

The Curvilinear Hydrodynamic 3-D (CH3D-WES) model is routinely applied in three-dimensional (3D) hydrodynamic and water quality modeling studies at the Engineering Research and Development Center (ERDC), Mississippi. Recent model improvements include the implementation of multiple grain size class sediment transport, grid wetting\\/drying, spatially and temporally varying wind and wave radiation stress gradient forcing. The practical application of the original single-block

Phu V. Luong; Raymond S. Chapman

2009-01-01

410

NASA Astrophysics Data System (ADS)

Measurements are reported on the step-response function, F( t), or magnetisation decay of five ferrofluid samples of magnetite in Isopar M with packing fractions ranging from 0.019 to 0.115. An alternative to the conventional method of measuring magnetisation decay involving the use of dc fields is used, with F( t) being obtained by means of a technique which utilises complex susceptibility data. The presence of a particle size distribution is accounted for with a measure of the particle distribution in each sample being determined by means of the 'approximate ellipse' technique.

Fannin, P. C.; Charles, S. W.

1994-09-01

411

Hydrodynamic Stability of Liquid-Propellant Combustion: Landau's Problem Revisited

NASA Technical Reports Server (NTRS)

Hydrodynamic, or Landau, instability in combustion is typically associated with the onset of wrinkling of a flame surface, corresponding to the formation of steady cellular structures as the stability threshold is crossed. As its name suggests, it stems from hydrodynamic effects connected with thermal expansion across the reaction region. In the context of liquid-propellant combustion, the classical models that originally predicted this phenomenon have been extended to include the important effects that arise from a dynamic dependence of the burning rate on the local pressure and temperature fields. Thus, the onset of Landau instability has now been shown to occur for sufficiently small negative values of the pressure sensitivity of the burning rate, significantly generalizing previous classical results for this problem that assumed a constant normal burning rate. It has also been shown that the onset of instability occurs for decreasing values of the disturbance wave number as the gravitational-acceleration parameter decreases. Consequently, in an appropriate weak-gravity limit, Landau instability becomes a long-wave phenomena associated with the formation of large cells on the liquid-propellant surface. Additionally, a pulsating form of hydrodynamic instability has been shown to occur as well, corresponding to the onset of temporal oscillations in the location of the liquid/gas interface. This instability occurs for sufficiently large negative values of the pressure sensitivity, and is enhanced by increasing values of the burning-rate temperature sensitivity. It is further shown that for sufficiently small values of this parameter, there exists a stable range of pressure sensitivities for steady, planar burning such that the classical cellular form of hydrodynamic instability and the more recent pulsating form of hydrodynamic instability can each occur as the corresponding stability threshold is crossed. For larger thermal sensitivities, however, the pulsating stability boundary evolves into a C-shaped curve in the (disturbance-wave number, pressure-sensitivity) plane, indicating loss of stability to pulsating perturbations for all sufficiently large disturbance wavelengths. It is thus concluded, based on characteristic parameter values that an equally likely form of hydrodynamic instability in liquid-propellant combustion is of a nonsteady, long-wave nature, distinct from the steady, cellular form originally predicted by Landau.

Margolis, S. B.

2001-01-01

412

Hydrodynamics of Fluid Vesicles

NASA Astrophysics Data System (ADS)

Dynamics of deformable mesoscopic objects determines rheology of many complex fluids such as emulsions, suspensions of droplets or bubbles, polymer solutions, blood, etc. I have investigated dynamics of giant vesicles in different types of flow and the rheological features of vesicle suspensions. The results provide consistent picture linking individual vesicle behavior in shear flow and interactions of the individual vesicles with each other with the rheological features of the vesicle suspensions. The investigations of a vesicle relaxation dynamics from one dynamically stable state to another after a sudden change of control parameters in elongation flow revealed new dynamical features of the vesicle membranes. The results on non-equilibrium dynamics of the vesicles provided a wave of theoretical interest to this problem, which was reflected to a number of new theories and numerical simulations [5-7,13]. Several new phenomena were discovered such as trembling motion, dynamical wrinkling instability, stretching transition of a tubule and pearling instability initiated by fluid stresses.

Kantsler, Vasiliy

413

Dust acoustic waves in quantum plasmas

The quantum hydrodynamic model for plasmas is employed to derive a new dispersion relation for the dust acoustic wave. It is found that the dispersion property of the latter is significantly affected by quantum corrections.

Shukla, P.K.; Ali, S. [Institut fuer Theoretische Physik IV, Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2005-11-15

414

National Weather Service Operational Dynamic Wave Model.

National Technical Information Service (NTIS)

In the early 1970's, the NWS Hydrologic Research Laboratory began developing a dynamic wave routing model based on an implicit finite difference solution of the complete one-dimensional St. Venant equations of unsteady flow. This hydrodynamic model, known...

D. L. Fread

1978-01-01

415

Numerical Hydrodynamics in Special Relativity

NASA Astrophysics Data System (ADS)

This review is concerned with a discussion of numerical methods for the solution of the equations of special relativistic hydrodynamics (SRHD). Particular emphasis is put on a comprehensive review of the application of high-resolution shock-capturing methods in SRHD. Results of a set of demanding test bench simulations obtained with different numerical SRHD methods are compared. Three applications (astrophysical jets, gamma-ray bursts and heavy ion collisions) of relativistic flows are discussed. An evaluation of various SRHD methods is presented, and future developments in SRHD are analyzed involving extension to general relativistic hydrodynamics and relativistic magneto-hydrodynamics. The review further provides FORTRAN programs to compute the exact solution of a 1D relativistic Riemann problem with zero and nonzero tangential velocities, and to simulate 1D relativistic flows in Cartesian Eulerian coordinates using the exact SRHD Riemann solver and PPM reconstruction.

Martí, José Maria; Müller, Ewald

2003-12-01

416

Hydrodynamics of fractal continuum flow.

A model of fractal continuum flow employing local fractional differential operators is suggested. The generalizations of the Green-Gauss divergence and Reynolds transport theorems for a fractal continuum are suggested. The fundamental conservation laws and hydrodynamic equations for an anisotropic fractal continuum flow are derived. Some physical implications of the long-range correlations in the fractal continuum flow are briefly discussed. It is noteworthy to point out that the fractal (quasi)metric defined in this paper implies that the flow of an isotropic fractal continuum obeying the Mandelbrot rule of thumb for intersection is governed by conventional hydrodynamic equations. PMID:22463270

Balankin, Alexander S; Elizarraraz, Benjamin Espinoza

2012-02-01

417

Hydrodynamics of fractal continuum flow

NASA Astrophysics Data System (ADS)

A model of fractal continuum flow employing local fractional differential operators is suggested. The generalizations of the Green-Gauss divergence and Reynolds transport theorems for a fractal continuum are suggested. The fundamental conservation laws and hydrodynamic equations for an anisotropic fractal continuum flow are derived. Some physical implications of the long-range correlations in the fractal continuum flow are briefly discussed. It is noteworthy to point out that the fractal (quasi)metric defined in this paper implies that the flow of an isotropic fractal continuum obeying the Mandelbrot rule of thumb for intersection is governed by conventional hydrodynamic equations.

Balankin, Alexander S.; Elizarraraz, Benjamin Espinoza

2012-02-01

418

Isogeometric analysis of Lagrangian hydrodynamics

NASA Astrophysics Data System (ADS)

Isogeometric analysis of Lagrangian shock hydrodynamics is proposed. The Euler equations of compressible hydrodynamics in the weak form are discretized using Non-Uniform Rational B-Splines (NURBS) in space. The discretization has all the advantages of a higher-order method, with the additional benefits of exact symmetry preservation and better per-degree-of-freedom accuracy. An explicit, second-order accurate time integration procedure, which conserves total energy, is developed and employed to advance the equations in time. The performance of the method is examined on a set of standard 2D and 3D benchmark examples, where good quality of the computational results is attained.

Bazilevs, Y.; Akkerman, I.; Benson, D. J.; Scovazzi, G.; Shashkov, M. J.

2013-06-01

419

Abnormal pressures as hydrodynamic phenomena

So-called abnormal pressures, subsurface fluid pressures significantly higher or lower than hydrostatic, have excited speculation about their origin since subsurface exploration first encountered them. Two distinct conceptual models for abnormal pressures have gained currency among earth scientists. The static model sees abnormal pressures generally as relict features preserved by a virtual absence of fluid flow over geologic time. The hydrodynamic model instead envisions abnormal pressures as phenomena in which flow usually plays an important role. This paper develops the theoretical framework for abnormal pressures as hydrodynamic phenomena, shows that it explains the manifold occurrences of abnormal pressures, and examines the implications of this approach. -from Author

Neuzil, C. E.

1995-01-01

420

Humboldt Bay Numerical Hydrodynamics amd Sedimentation Study.

National Technical Information Service (NTIS)

A study was done on the hydrodynamics and sedimentation of Humboldt Bay, California. This was done to determine the effects of channel deepening and realignment on the currents and sedimentation patterns in the area. The hydrodynamics and sedimentation we...

R. A. Evans

1994-01-01

421

Toward a Fully Consistent Radiation Hydrodynamics.

National Technical Information Service (NTIS)

Dimitri Mihalas set the standard for all work in radiation hydrodynamics since 1984. The present contribution builds on 'Foundations of Radiation Hydrodynamics' to explore the relativistic effects that have prevented having a consistent non-relativistic t...

J. Castor

2009-01-01

422

Hydrodynamic dispersion in porous materials

This study considers some aspects of the hydrodynamic dispersion of tracer which occurs under the combined influence of molecular diffusion and convection when a fluid flows through a finite column of porous material. In particular, the study discusses (1) the use of the principle of superposition to obtain breakthrough curves for pulsed and periodic inputs of tracer, (2) the form

D. A. ROSE

1977-01-01

423

Hydrodynamic Interactions Between Two Bodies

On the basis of model tests, potential flow theory, and viscous Computational Fluid Dynamics (CFD) method, the hydrodynamic interactions between two underwater bodies were investigated to determine the influencing factors, changing rule, interaction mechanism, and appropriate methods describing them. Some special phenomena were discovered in two series of near-wall interaction experiments. The mathematical model and predicting methods were presented for

Li CHENG

2007-01-01

424

Smoothed Particle Hydrodynamics Stability Analysis

SPH (smoothed particle hydrodynamics) is a gridless Lagrangian technique which is appealing as a possible alternative to numerical techniques currently used to analyze large deformation events. Recent tests of the standard SPH method using the cubic B-spline kernel indicated the possibility of an instability in the tensile regime, even though no such difficulties were observed in compression. A von Neumann

J. W. Swegle; D. L. Hicks; S. W. Attaway

1995-01-01

425

Hydrodynamic instabilities in inertial fusion

This report discusses topics on hydrodynamics instabilities in inertial confinement: linear analysis of Rayleigh-Taylor instability; ablation-surface instability; bubble rise in late-stage Rayleigh-Taylor instability; and saturation and multimode interactions in intermediate-stage Rayleigh-Taylor instability.

Hoffman, N.M.

1994-09-01

426

Hydrodynamics of galactic dark matter

We consider simple hydrodynamical models of galactic dark matter in which the galactic halo is a self-gravitating and self-interacting gas that dominates the dynamics of the galaxy. Modelling this halo as a spherically symmetric and static perfect fluid satisfying the field equations of general relativity, visible baryonic matter can be treated as 'test particles' in the geometry of this field.

Luis G. Cabral-Rosetti; Tonatiuh Matos; Darío Nuñez; Roberto A. Sussman

2002-01-01

427

Hydrodynamics of galactic dark matter

We consider simple hydrodynamical models of galactic dark matter in which the galactic halo is a self-gravitating and self-interacting gas that dominates the dynamics of the galaxy. Modelling this halo as a spherically symmetric and static perfect fluid satisfying the field equations of general relativity, visible baryonic matter can be treated as 'test particles' in the geometry of this field.

Roberto A Sussman

428

Web-based hydrodynamics computing

Proteins are long chains of amino acids that have a definite 3-d conformation and the shape of each protein is vital to its function. Since proteins are normally in solution, hydrodynamics (describes the movement of solvent around a protein as a function of shape and size of the molecule) can be used to probe the size and shape of proteins

Alan Shimoide; Luping Lin; Tracie-Lynne Hong; Ilmi Yoon; Sergio R. Aragon

2004-01-01

429

Hydrodynamics of galactic dark matter

We consider simple hydrodynamical models of galactic dark matter in which the galactic halo is a self-gravitating and self-interacting gas that dominates the dynamics of the galaxy. Modelling this halo as a spherically symmetric and static perfect fluid satisfying the field equations of general relativity, visible baryonic matter can be treated as ‘test particles’ in the geometry of this field.

Luis G. Cabral-Rosetti; Tonatiuh Matos; Darío Nuñez; Roberto A. Sussman

2002-01-01

430

Hydrodynamic loads on a three-dimensional body in a narrow tank

An integral equation approach is utilized to investigate the influence of tank walls on the hydrodynamic forces experienced by an arbitrary three-dimensional body situated in a narrow wave tank. An appropriate three-dimensional Green function which satisfies the tank-wall boundary conditions is developed to facilitate the solution. Numerical results are presented for truncated cylinders of circular and elliptic cross section which illustrate the effect of the tank walls on the wave-induced forces. The numerical results indicate that the hydrodynamic loads on a three-dimensional body in a narrow tank may be quite different from those on the same body in the open sea.

Vazquez, J.H.; Williams, A.N. (Univ. of Houston, TX (United States). Dept. of Civil and Environmental Engineering)

1994-08-01

431

Research on the unsteady hydrodynamic characteristics of vertical axis tidal turbine

NASA Astrophysics Data System (ADS)

The unsteady hydrodynamic characteristics of vertical axis tidal turbine are investigated by numerical simulation based on viscous CFD method. The starting mechanism of the turbine is revealed through analyzing the interaction of its motion and dynamics during starting process. The operating hydrodynamic characteristics of the turbine in wave-current condition are also explored by combining with the linear wave theory. According to possible magnification of the cyclic loads in the maximum power tracking control of vertical axis turbine, a novel torque control strategy is put forward, which can improve the structural characteristics significantly without effecting energy efficiency.

Zhang, Xue-wei; Zhang, Liang; Wang, Feng; Zhao, Dong-ya; Pang, Cheng-yan

2014-03-01

432

Hydrodynamic analysis of time series

NASA Astrophysics Data System (ADS)

It was proved that balance equations for systems with corpuscular structure can be derived if a kinematic description by piece-wise analytic functions is available [1]. For example, the hydrodynamic equations for one-dimensional systems of inelastic particles, derived in [2], were used to prove the inconsistency of the Fourier law of heat with the microscopic structure of the system. The hydrodynamic description is also possible for single particle systems. In this case, averages of physical quantities associated with the particle, over a space-time window, generalizing the usual ``moving averages'' which are performed on time intervals only, were shown to be almost everywhere continuous space-time functions. Moreover, they obey balance partial differential equations (continuity equation for the 'concentration', Navier-Stokes equation, a. s. o.) [3]. Time series can be interpreted as trajectories in the space of the recorded parameter. Their hydrodynamic interpretation is expected to enable deterministic predictions, when closure relations can be obtained for the balance equations. For the time being, a first result is the estimation of the probability density for the occurrence of a given parameter value, by the normalized concentration field from the hydrodynamic description. The method is illustrated by hydrodynamic analysis of three types of time series: white noise, stock prices from financial markets and groundwater levels recorded at Krauthausen experimental field of Forschungszentrum Jülich (Germany). [1] C. Vamo?, A. Georgescu, N. Suciu, I. Turcu, Physica A 227, 81-92, 1996. [2] C. Vamo?, N. Suciu, A. Georgescu, Phys. Rev E 55, 5, 6277-6280, 1997. [3] C. Vamo?, N. Suciu, W. Blaj, Physica A, 287, 461-467, 2000.

Suciu, N.; Vamos, C.; Vereecken, H.; Vanderborght, J.

2003-04-01

433

A theoretical study of hydrodynamic cavitation

The optimization of hydrodynamic cavitation as an AOP requires identifying the key parameters and studying their effects on the process. Specific simulations of hydrodynamic bubbles reveal that time scales play a major role on the process. Rarefaction\\/compression periods generate a number of opposing effects which have demonstrated to be quantitatively different from those found in ultrasonic cavitation. Hydrodynamic cavitation can

S. Arrojo; Y. Benito

2008-01-01

434

The quantum hydrodynamic model for semiconductor devices

The classical hydrodynamic equations can be extended to include quantum effects by incorporating the first quantum corrections. The full three-dimensional quantum hydrodynamic (QHD) model is derived for the first time by a moment expansion of the Wigner-Boltzmann equations. The QHD conservation laws have the same form as the classical hydrodynamic equations, but the energy density and stress tensor have additional

Carl L. Gardner

1994-01-01

435

HEATING OF THE SOLAR CORONA BY GRAVITY WAVES

ABS>A new type of hydrodynamic-wave heating is proposed for the solar ; corona. It is shown that internal gravity waves are preferentially generated by ; the convection zone and are easily transmitted to the corona. Acoustic waves ; with frequency characteristic of the photospheric granules cannot be transmitted ; through the reversing layer. The gravity waves are shown to dissipate

William A. Whitaker

1963-01-01

436

Hydrodynamics of maneuvering bodies: LDRD final report

The objective of the ``Hydrodynamics of Maneuvering Bodies`` LDRD project was to develop a Lagrangian, vorticity-based numerical simulation of the fluid dynamics associated with a maneuvering submarine. Three major tasks were completed. First, a vortex model to simulate the wake behind a maneuvering submarine was completed, assuming the flow to be inviscid and of constant density. Several simulations were performed for a dive maneuver, each requiring less than 20 cpu seconds on a workstation. The technical details of the model and the simulations are described in a separate document, but are reviewed herein. Second, a gridless method to simulate diffusion processes was developed that has significant advantages over previous Lagrangian diffusion models. In this model, viscous diffusion of vorticity is represented by moving vortices at a diffusion velocity, and expanding the vortices as specified by the kinematics for a compressible velocity field. This work has also been documented previously, and is only reviewed herein. The third major task completed was the development of a vortex model to describe inviscid internal wave phenomena, and is the focus of this document. Internal wave phenomena in the stratified ocean can affect an evolving wake, and thus must be considered for naval applications. The vortex model for internal wave phenomena includes a new formulation for the generation of vorticity due to fluid density variations, and a vortex adoption algorithm that allows solutions to be carried to much longer times than previous investigations. Since many practical problems require long-time solutions, this new adoption algorithm is a significant step toward making vortex methods applicable to practical problems. Several simulations are described and compared with previous results to validate and show the advantages of the new model. An overview of this project is also included.

Kempka, S.N.; Strickland, J.H.

1994-01-01

437

Hydrodynamics of maneuvering bodies: LDRD Final Report

NASA Astrophysics Data System (ADS)

The objective of the 'Hydrodynamics of Maneuvering Bodies' LDRD project was to develop a Lagrangian, vorticity-based numerical simulation of the fluid dynamics associated with a maneuvering submarine. Three major tasks were completed. First, a vortex model to simulate the wake behind a maneuvering submarine was completed, assuming the flow to be inviscid and of constant density. Several simulations were performed for a dive maneuver, each requiring less than 20 cpu seconds on a workstation. The technical details of the model and the simulations are described in a separate document, but are reviewed herein. Second, a gridless method to simulate diffusion processes was developed that has significant advantages over previous Lagrangian diffusion models. In this model, viscous diffusion of vorticity is represented by moving vortices at a diffusion velocity, and expanding the vortices as specified by the kinematics for a compressible velocity field. This work was also documented previously and is only reviewed herein. The third major task completed was the development of a vortex model to describe inviscid internal wave phenomena and is the focus of this document. Internal wave phenomena in the stratified ocean can affect an evolving wake and thus, must be considered for naval applications. The vortex model for internal wave phenomena includes a new formulation for the generation of vorticity due to fluid density variations and a vortex adoption algorithm that allows solutions to be carried to much longer times than previous investigations. Since many practical problems require long-time solutions, this new adoption algorithm is a significant step toward making vortex methods applicable to practical problems. Several simulations are described and compared with previous results to validate and show the advantages of the new model. An overview of this project is also included.

Kempka, S. N.; Strickland, J. H.

1994-01-01

438

Hydrodynamic variability on megatidal beaches, Normandy, France

NASA Astrophysics Data System (ADS)

Several experiments aimed at characterising the hydrodynamics of megatidal beaches outside the surf zone were carried out between 1990 and 1994 on the Cotentin coast of the Cherbourg Peninsula in Normandy. The database was established from the records of several electromagnetic current meters and pressure sensors and from field surveys. The mean spring tidal range on these beaches varies between 9.3 and 11.4 m. The results show the prevalence of strong longshore currents, with velocities up to 0.5 m s -1, on the low- and mid-tidal beach zones. Mostly oriented northward, these currents reflect both a progressive tidal wave and a strong longshore gradient in water level between the Channel Islands embayment and the English Channel. While varying largely during a typical tidal cycle, these longshore velocities are maximum at high tide, reflecting the progressive nature of the tides. This high-tide maximum velocity increases by a factor of 1.5 between the mean tide and mean spring tide, and between the mid- and low-tidal zones due to bed friction effects. Cross-shore velocities are generally weak (<0.1 m s -1), but sometimes stronger in smaller water depths. In the low-tidal zone, they are commonly oriented onshore at the beginning of the rising tide and offshore during the falling tide. This circulation results from a west-east cross-shore gradient in water level that is particularly important around the mean water level. Towards high tides, weak offshore steady flows were observed in the presence of waves. Site-specific relationships were defined in order to characterise the modulation of significant wave height by sea level fluctuations both on the shoreface and in the intertidal zone. The water depth variability during the tidal cycle induces fluctuations in the dissipation by bottom friction, resulting in wave height changes. The influence of tidal currents on the wave height proved to be very small in this context. The tidal fluctuations also influence the instantaneous near-bed currents induced by simultaneous action of non-breaking waves and the tides. During stormy conditions, wave-induced gravity orbital motions dominate the steady flows in the mid-tidal zone, outside the surf zone. At this location, the shallow water friction effect results in weak steady longshore currents, and low water depths explain strong orbital motions. The opposite conditions prevail in the low-tidal zone, where the steady tidal currents are stronger than gravity orbital velocities during a few hours around high tide. Outside this period, with the decrease in water depth and in steady current intensity due to friction effects, the tidal and gravity wave-induced currents have comparable intensities. In both the low- and mid-tidal zones, infragravity motions are weak outside the surf zone. The foregoing results show that outside the surf zone, these megatidal beaches are characterised by wave-dominated mid-tidal zones and tide-dominated low-tidal zones during spring tides. We suggest the term "mixed wave-tide-dominated" for these beaches with very large tidal ranges.

Levoy, Franck; Monfort, Olivier; Larsonneur, Claude

2001-04-01

439

Quantum hydrodynamics: application to N-dimensional reactive scattering.

The quantum hydrodynamic equations associated with the de Broglie-Bohm formulation of quantum mechanics are solved using a new methodology which gives an accurate, unitary, and stable propagation of a time dependent quantum wave packet [B. K. Kendrick, J. Chem. Phys. 119, 5805 (2003)]. The methodology is applied to an N-dimensional model chemical reaction with an activation barrier. A parallel version of the methodology is presented which is designed to run on massively parallel supercomputers. The computational scaling properties of the parallel code are investigated both as a function of the number of processors and the dimension N. A decoupling scheme is introduced which decouples the multidimensional quantum hydrodynamic equations into a set of uncoupled one-dimensional problems. The decoupling scheme dramatically reduces the computation time and is highly parallelizable. Furthermore, the computation time is shown to scale linearly with respect to the dimension N=2,...,100. PMID:15281844

Kendrick, Brian K

2004-08-01

440

Hydrodynamic Fluctuations in Confined Particle-Laden Fluids

NASA Astrophysics Data System (ADS)

We address the collective dynamics of non-Brownian particles cruising in a confined microfluidic geometry and provide a comprehensive characterization of their spatiotemporal density fluctuations. We show that density excitations freely propagate at all scales, and in all directions even though the particles are neither affected by potential forces nor by inertia. We introduce a kinetic theory which quantitatively accounts for our experimental findings, demonstrating that the fluctuation spectrum of this nonequilibrium system is shaped by the combination of truly long-range hydrodynamic interactions and local collisions. We also demonstrate that the free propagation of density waves is a generic phenomenon which should be observed in a much broader range of hydrodynamic systems.

Desreumaux, Nicolas; Caussin, Jean-Baptiste; Jeanneret, Raphael; Lauga, Eric; Bartolo, Denis

2013-09-01

441

Hydrodynamic fluctuations in confined particle-laden fluids.

We address the collective dynamics of non-Brownian particles cruising in a confined microfluidic geometry and provide a comprehensive characterization of their spatiotemporal density fluctuations. We show that density excitations freely propagate at all scales, and in all directions even though the particles are neither affected by potential forces nor by inertia. We introduce a kinetic theory which quantitati