Nowak, J; Wiekhorst, F; Trahms, L; Odenbach, S
2014-04-30
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
Commercial applications of ferrofluids
K. Raj; R. Moskowitz
1990-01-01
Ferrofluids have been in the commercial arena for over two decades. In this paper, the most advanced, successful commercial applications of ferrofluids are discussed. These applications center around the tribological characteristics of ferrofluids, e.g., sealing, damping and hydrodynamic bearings. Also, an account of some lesser known applications is presented.
NASA Astrophysics Data System (ADS)
Bush, John W. M.
2015-01-01
Yves Couder, Emmanuel Fort, and coworkers recently discovered that a millimetric droplet sustained on the surface of a vibrating fluid bath may self-propel through a resonant interaction with its own wave field. This article reviews experimental evidence indicating that the walking droplets exhibit certain features previously thought to be exclusive to the microscopic, quantum realm. It then reviews theoretical descriptions of this hydrodynamic pilot-wave system that yield insight into the origins of its quantum-like behavior. Quantization arises from the dynamic constraint imposed on the droplet by its pilot-wave field, and multimodal statistics appear to be a feature of chaotic pilot-wave dynamics. I attempt to assess the potential and limitations of this hydrodynamic system as a quantum analog. This fluid system is compared to quantum pilot-wave theories, shown to be markedly different from Bohmian mechanics and more closely related to de Broglie's original conception of quantum dynamics, his double-solution theory, and its relatively recent extensions through researchers in stochastic electrodynamics.
Bush, John W. M.
Yves Couder, Emmanuel Fort, and coworkers recently discovered that a millimetric droplet sustained on the surface of a vibrating fluid bath may self-propel through a resonant interaction with its own wave field. This article ...
Falcon, Eric
Observation of Axisymmetric Solitary Waves on the Surface of a Ferrofluid E. Bourdin, J.-C. Bacri 2010) We report the first observation of axisymmetric solitary waves on the surface of a cylindrical the magnetic and capillary forces, both elevation and depression solitary waves are observed with profiles
NASA Technical Reports Server (NTRS)
1993-01-01
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.
Wave Turbulence on the Surface of a Ferrofluid in a Magnetic Field Francois Boyer and Eric Falcon*
Falcon, Eric
instability [10], the labyrinthine instabil- ity, magnetic levitation [11]. In contrast with usual liquidsWave Turbulence on the Surface of a Ferrofluid in a Magnetic Field Franc¸ois Boyer and Eric Falcon normal magnetic field. We show that magnetic surface waves arise only above a critical field. The power
Oscillatory hydrodynamic flow induced by chemical waves
NASA Astrophysics Data System (ADS)
Miike, Hidetoshi; Müller, Stefan C.; Hess, Benno
1988-05-01
Hydrodynamic flows in a reactive liquid induced by the propagation of waves of chemical activity are investigated for the ferroin-catalyzed Belousov-Zhabotinskii reaction in thin layers by microscope video imaging techniques. The motion of added polystyrene spheres is observed with laser light illumination. Oscillations in the hydrodynamic flow were detected in rotating spiral waves with an open liquid/gas interface.
Simple Waves in Ideal Radiation Hydrodynamics
Bryan M. Johnson
2008-11-24
In the dynamic diffusion limit of radiation hydrodynamics, advection dominates diffusion; the latter primarily affects small scales and has negligible impact on the large scale flow. The radiation can thus be accurately regarded as an ideal fluid, i.e., radiative diffusion can be neglected along with other forms of dissipation. This viewpoint is applied here to an analysis of simple waves in an ideal radiating fluid. It is shown that much of the hydrodynamic analysis carries over by simply replacing the material sound speed, pressure and index with the values appropriate for a radiating fluid. A complete analysis is performed for a centered rarefaction wave, and expressions are provided for the Riemann invariants and characteristic curves of the one-dimensional system of equations. The analytical solution is checked for consistency against a finite difference numerical integration, and the validity of neglecting the diffusion operator is demonstrated. An interesting physical result is that for a material component with a large number of internal degrees of freedom and an internal energy greater than that of the radiation, the sound speed increases as the fluid is rarefied. These solutions are an excellent test for radiation hydrodynamic codes operating in the dynamic diffusion regime. The general approach may be useful in the development of Godunov numerical schemes for radiation hydrodynamics.
SIMPLE WAVES IN IDEAL RADIATION HYDRODYNAMICS
Johnson, Bryan M.
2009-03-10
In the dynamic diffusion limit of radiation hydrodynamics, advection dominates diffusion; the latter primarily affects small scales and has negligible impact on the large-scale flow. The radiation can thus be accurately regarded as an ideal fluid, i.e., radiative diffusion can be neglected along with other forms of dissipation. This viewpoint is applied here to an analysis of simple waves in an ideal radiating fluid. It is shown that much of the hydrodynamic analysis carries over by simply replacing the material sound speed, pressure, and adiabatic index with the values appropriate for a radiating fluid. A complete analysis is performed for a centered rarefaction wave, and expressions are provided for the Riemann invariants and characteristic curves of the one-dimensional system of equations. The analytical solution is checked for consistency against a finite difference numerical integration, and the validity of neglecting the diffusion operator is demonstrated. An interesting physical result is that for a material component with a large number of internal degrees of freedom and an internal energy greater than that of the radiation, the sound speed increases as the fluid is rarefied. These solutions are an excellent test for radiation hydrodynamic codes operating in the dynamic diffusion regime. The general approach may be useful in the development of Godunov numerical schemes for radiation hydrodynamics.
Simple Waves in Ideal Radiation Hydrodynamics
Johnson, B M
2008-09-03
In the dynamic diffusion limit of radiation hydrodynamics, advection dominates diffusion; the latter primarily affects small scales and has negligible impact on the large scale flow. The radiation can thus be accurately regarded as an ideal fluid, i.e., radiative diffusion can be neglected along with other forms of dissipation. This viewpoint is applied here to an analysis of simple waves in an ideal radiating fluid. It is shown that much of the hydrodynamic analysis carries over by simply replacing the material sound speed, pressure and index with the values appropriate for a radiating fluid. A complete analysis is performed for a centered rarefaction wave, and expressions are provided for the Riemann invariants and characteristic curves of the one-dimensional system of equations. The analytical solution is checked for consistency against a finite difference numerical integration, and the validity of neglecting the diffusion operator is demonstrated. An interesting physical result is that for a material component with a large number of internal degrees of freedom and an internal energy greater than that of the radiation, the sound speed increases as the fluid is rarefied. These solutions are an excellent test for radiation hydrodynamic codes operating in the dynamic diffusion regime. The general approach may be useful in the development of Godunov numerical schemes for radiation hydrodynamics.
NASA Astrophysics Data System (ADS)
Odenbach, Professor Stefan
2006-09-01
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
Hydrodynamic principles of wave power extraction.
Mei, Chiang C
2012-01-28
The hydrodynamic principles common to many wave power converters are reviewed via two representative systems. The first involves one or more floating bodies, and the second water oscillating in a fixed enclosure. It is shown that the prevailing basis is impedance matching and resonance, for which the typical analysis can be illustrated for a single buoy and for an oscillating water column. We then examine the mechanics of a more recent design involving a compact array of small buoys that are not resonated. Its theoretical potential is compared with that of a large buoy of equal volume. A simple theory is also given for a two-dimensional array of small buoys in well-separated rows parallel to a coast. The effects of coastline on a land-based oscillating water column are examined analytically. Possible benefits of moderate to large column sizes are explored. Strategies for broadening the frequency bandwidth of high efficiency by controlling the power-takeoff system are discussed. PMID:22184659
EQUILIBRIUM HYDRODYNAMIC VARIABLES BEHIND A NORMAL SHOCK WAVE IN HYDROGEN
1958-01-01
A complete calculation was performed on the hydrodynamic variables for ; shock Mach numbers up to and beyond the point where hydrogen becomes completely ; ionized. A set of curves is presented for initial pressures of 10â»Â², 10\\/; sup -3\\/, and 10â»â´ atmospheres including density ratio across the shock ; wave, the temperature behind the shock wave, and the degree
Anderson, Mary Elizabeth
2011-10-21
Wave attenuation by vegetation is a highly dynamic process and its quantification is important for accurately understanding and predicting coastal hydrodynamics. However, the influence of vegetation on wave dissipation is not yet fully established...
Advances in ferrofluid technology
K. Raj; B. Moskowitz; R. Casciari
1995-01-01
Traditional ferrofluid products such as multistage rotary seals, exclusion seals, inertia dampers and loudspeakers are now a well established industry. Additionally, in the last few years a number of new applications have emerged such as ferrofluid steppers, gauges and sensors. The purpose of this paper is to review recent advances in ferrofluid technology both in the conventional and in new
Sound damping in ferrofluids: magnetically enhanced compressional viscosity.
Müller, Hanns Walter; Jiang, Yimin; Liu, Mario
2003-03-01
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
Nonlinear Generalized Hydrodynamic Wave Equations in Strongly Coupled Dusty Plasmas
Veeresha, B. M.; Sen, A.; Kaw, P. K. [Institute for Plasma Research, Bhat, Gandhinagar-382428 (India)
2008-09-07
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.
EQUILIBRIUM HYDRODYNAMIC VARIABLES BEHIND A REFLECTED SHOCK WAVE IN HYDROGEN
1959-01-01
Hydrodynamic variables such as density ratio, pressure ratio, ; temperature, fraction of dissociation and ionization, and the reflected shock ; velocity were calculated for a reflected shock wave in hydrogen for one dimension. ; The data are presented as families of curves of these variables plotted against ; the initial shock Mach number for a range of unity to 200
Ferrofluids: Thermophysical properties and formation of microstructures
NASA Astrophysics Data System (ADS)
Mousavi Khoeini, NargesSadat Susan
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
Hydrodynamic Waves in an Anomalous Charged Fluid
Abbasi, Navid; Rezaei, Zahra
2015-01-01
We study the collective excitations in a relativistic fluid with an anomalous conserved charge. In $3+1$ dimensions, in addition to two ordinary sound modes we find two propagating modes in presence of an external magnetic field: one with a velocity proportional to the coefficient of gauge-gravitational anomaly coefficient and the other with a velocity which depends on both chiral anomaly and the gauge gravitational anomaly coefficients. While the former is the Chiral Alfv\\'en wave recently found in arXiv:1505.05444, the latter is a new type of collective excitations originated from the density fluctuations. We refer to these modes as the Type-M and Type-D chiral Alfv\\'en waves respectively. We show that the Type-M Chiral Alfv\\'en mode is split into two chiral Alfv\\'en modes when taking into account the effect of dissipation processes in the fluid. In 1+1 dimensions we find only one propagating mode associated with the anomalous effects. We explicitly compute the velocity of this wave and show that in contras...
Hydrodynamic Waves in an Anomalous Charged Fluid
Navid Abbasi; Ali Davody; Zahra Rezaei
2015-09-29
We study the collective excitations in a relativistic fluid with an anomalous conserved charge. In $3+1$ dimensions, in addition to two ordinary sound modes we find two propagating modes in presence of an external magnetic field: one with a velocity proportional to the coefficient of gauge-gravitational anomaly coefficient and the other with a velocity which depends on both chiral anomaly and the gauge gravitational anomaly coefficients. While the former is the Chiral Alfv\\'en wave recently found in arXiv:1505.05444, the latter is a new type of collective excitations originated from the density fluctuations. We refer to these modes as the Type-M and Type-D chiral Alfv\\'en waves respectively. We show that the Type-M Chiral Alfv\\'en mode is split into two chiral Alfv\\'en modes when taking into account the effect of dissipation processes in the fluid. In 1+1 dimensions we find only one propagating mode associated with the anomalous effects. We explicitly compute the velocity of this wave and show that in contrast to $3+1$ dimensions, no external field is needed for this mode to propagate.
Hydrodynamic shock wave studies within a kinetic Monte Carlo approach
NASA Astrophysics Data System (ADS)
Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Howell, Jim; Pickett, Rodney; Staber, Alec; Strother, Terrance
2014-06-01
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.
Hydrodynamic Modes of a holographic $p-$ wave superfluid
Raul E. Arias; Ignacio Salazar Landea
2014-11-04
In this work we analyze the hydrodynamics of a $p-$ wave superfluid on its strongly coupled regime by considering its holographic description. We obtain the poles of the retarded Green function through the computation of the quasi-normal modes of the dual AdS black hole background finding diffusive, pseudo-diffusive and sound modes. For the sound modes we compute the speed of sound and its attenuation as function of the temperature. For the diffusive and pseudo-diffusive modes we find that they acquire a non-zero real part at certain finite momentum.
RADIATIVE HYDRODYNAMIC SIMULATIONS OF ACOUSTIC WAVES IN SUNSPOTS
Bard, S.; Carlsson, M.
2010-10-10
We investigate the formation and evolution of the Ca II H line in a sunspot. The aim of our study is to establish the mechanisms underlying the formation of the frequently observed brightenings of small regions of sunspot umbrae known as 'umbral flashes'. We perform fully consistent NLTE radiation hydrodynamic simulations of the propagation of acoustic waves in sunspot umbrae and conclude that umbral flashes result from increased emission of the local solar material during the passage of acoustic waves originating in the photosphere and steepening to shock in the chromosphere. To quantify the significance of possible physical mechanisms that contribute to the formation of umbral flashes, we perform a set of simulations on a grid formed by different wave power spectra, different inbound coronal radiation, and different parameterized chromospheric heating. Our simulations show that the waves with frequencies in the range 4.5-7.0 mHz are critical to the formation of the observed blueshifts of umbral flashes while waves with frequencies below 4.5 mHz do not play a role despite their dominance in the photosphere. The observed emission in the Ca II H core between flashes only occurs in the simulations that include significant inbound coronal radiation and/or extra non-radiative chromospheric heating in addition to shock dissipation.
Smoothed Particle Hydrodynamics for water wave propagation in a channel
NASA Astrophysics Data System (ADS)
Omidvar, Pourya; Norouzi, Hossein; Zarghami, Ahad
2015-01-01
In this paper, Smoothed Particle Hydrodynamics (SPH) is used to simulate the propagation of waves in an intermediate depth water channel. The major advantage of using SPH is that no special treatment of the free surface is required, which is advantageous for simulating highly nonlinear flows with possible wave breaking. The SPH method has an option of different formulations with their own advantages and drawbacks to be implemented. Here, we apply the classical and Arbitrary Lagrange-Euler (ALE) formulation for wave propagation in a water channel. The classical SPH should come with an artificial viscosity which stabilizes the numerical algorithm and increases the accuracy. Here, we will show that the use of classical SPH with an artificial viscosity may cause the waves in the channel to decay. On the other hand, we will show that using the ALE-SPH algorithm with a Riemann solver is more stable, and in addition to producing the pressure fields with much less numerical noise, the waves propagate in the channel without dissipation.
Hydrodynamic view of wave-packet interference: quantum caves.
Chou, Chia-Chun; Sanz, Angel S; Miret-Artés, Salvador; Wyatt, Robert E
2009-06-26
Wave-packet interference is investigated within the complex quantum Hamilton-Jacobi formalism using a hydrodynamic description. Quantum interference leads to the formation of the topological structure of quantum caves in space-time Argand plots. These caves consist of the vortical and stagnation tubes originating from the isosurfaces of the amplitude of the wave function and its first derivative. Complex quantum trajectories display counterclockwise helical wrapping around the stagnation tubes and hyperbolic deflection near the vortical tubes. The string of alternating stagnation and vortical tubes is sufficient to generate divergent trajectories. Moreover, the average wrapping time for trajectories and the rotational rate of the nodal line in the complex plane can be used to define the lifetime for interference features. PMID:19659057
A hydrodynamic view of wave packet interference: Quantum caves
Chou, C -C; Miret-Artés, S; Wyatt, R E
2008-01-01
The interference of quantum wave packets is investigated within the complex quantum Hamilton-Jacobi formalism using a hydrodynamic description. Interference plays an important role in quantum mechanics, and it leads to the formation and topological structure of quantum caves in space-time Argand plots. Quantum caves consist of the vortical and stagnation tubes originating from the isosurfaces of the amplitude of the wave function and its first derivative. Complex quantum trajectories display helical wrapping around the stagnation tubes and hyperbolic deflection near the vortical tubes. Trajectories launched from different positions wind around the same stagnation curve for a while and then depart as time progresses, analogous to a resonance process. These trajectories thus show a type of long-range correlation in complex space. It is shown that the complex quantum trajectory method provides a novel perspective for analysis and interpretation of quantum phenomena.
Hydrodynamic View of Wave-Packet Interference: Quantum Caves
C. -C. Chou; A. S. Sanz; S. Miret-Artes; R. E. Wyatt
2009-06-24
Wave-packet interference is investigated within the complex quantum Hamilton-Jacobi formalism using a hydrodynamic description. Quantum interference leads to the formation of the topological structure of quantum caves in space-time Argand plots. These caves consist of the vortical and stagnation tubes originating from the isosurfaces of the amplitude of the wave function and its first derivative. Complex quantum trajectories display counterclockwise helical wrapping around the stagnation tubes and hyperbolic deflection near the vortical tubes. The string of alternating stagnation and vortical tubes is sufficient to generate divergent trajectories. Moreover, the average wrapping time for trajectories and the rotational rate of the nodal line in the complex plane can be used to define the lifetime for interference features.
Detecting shock waves in cosmological smoothed particle hydrodynamics simulations
Christoph Pfrommer; Volker Springel; Torsten A. Ensslin; Martin Jubelgas
2006-03-19
We develop a formalism for the identification and accurate estimation of the strength of structure formation shocks during cosmological smoothed particle hydrodynamics simulations. Shocks not only play a decisive role for the thermalization of gas in virialising structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. Our formalism is applicable both to ordinary non-relativistic thermal gas, and to plasmas composed of CRs and thermal gas. To this end, we derive an analytical solution to the one-dimensional Riemann shock tube problem for a composite plasma of CRs and thermal gas. We apply our methods to study the properties of structure formation shocks in high-resolution hydrodynamic simulations of the LCDM model. We find that most of the energy is dissipated in weak internal shocks with Mach numbers M~2 which are predominantly central flow shocks or merger shock waves traversing halo centres. Collapsed cosmological structures are surrounded by external shocks with much higher Mach numbers up to M~1000, but they play only a minor role in the energy balance of thermalization. We show that after the epoch of cosmic reionisation the Mach number distribution is significantly modified by an efficient suppression of strong external shock waves due to the associated increase of the sound speed of the diffuse gas. Invoking a model for CR acceleration in shock waves, we find that the average strength of shock waves responsible for CR energy injection is higher than that for shocks that dominate the thermalization of the gas. When combined with radiative dissipation and star formation, our formalism can also be used to study CR injection by supernova shocks, or to construct models for shock-induced star formation in the interstellar medium. (abridged)
NASA Astrophysics Data System (ADS)
Benson, P.; Meredith, P.; Platzman, E.; White, R.
2003-12-01
Pore fabric geometry is a key feature of sedimentary rocks. Anisotropy arising from pore fabric has been commonly studied in terms of acoustic-wave (seismic) anisotropy, fluid flow (permeability) anisotropy and magnetic anisotropy (Anisotropy of Magnetic Susceptibility - AMS). However, combined approaches are relatively few, and often concentrate on grain fabric AMS. Here, we present results from an experimental study in which the AMS technique is used to determine the average 3D void space geometry in porous rock saturated with a high susceptibility magnetic ferrofluid. Using this approach, we independently show that the acoustic wave anisotropy and permeability anisotropy are well described by knowledge of the pore fabric anisotropy. We also demonstrate that pressure produces marked changes in both permeability and acoustic wave velocity, and that pore fabric is a useful tool with which to explain such changes. Measurements were made on Crab Orchard sandstone (COS) and Bentheim sandstone (BHS), chosen specifically for their contrasting strong (COS) and weak (BHS) anisotropy. COS is fine-grained and exhibits layering on a mm scale. It has a high cement content, resulting in a porosity of 4.5%. By contrast, BHS comprises 95% quartz grains in an open structure, resulting in a porosity of 22%. AMS was determined by measuring the susceptibility of ferrofluid saturated samples in 15 different orientations. A least squares ellipsoidal fit was then applied to this data to calculate the principal directions. Comparative elastic wave velocity measurements were then made in 10 degree increments around the circumferences of sets of three orthogonal cores. An equivalent 3D velocity ellipsoid was then determined, allowing for direct comparison of the velocity and AMS data. The error in using an ellipsoidal fit, rather than a fourth rank tensor, is estimated as less than 1.5%; approximately equal to the error in velocity measurement. Finally, measurements of permeability anisotropy, together with simultaneous ultrasonic velocity measurements, were made in a servo-controlled permeameter at effective pressures from 5 to 90MPa. In general, the permeability of COS parallel to bedding is some 3 times higher than that normal to bedding; whereas the permeability of BHS exhibits no discernible anisotropy. We find a strong positive correlation between the principal directions given by pore space AMS, velocity anisotropy, and permeability anisotropy. P-wave velocity anisotropy on dry samples was 19% and 5% for COS and BHS, respectively. This compares with a pore fabric anisotropy of 3.8% (COS) and 1.4% (BHS). The permeability of COS decreases from 75 to 8 mDarcy as effective pressure is increased from 5 to 90 MPa, a corresponding increase in acoustic wave velocity is also observed. BHS has a considerably higher permeability (830 mDarcy), but this changes little as pressure is increased. Our results clearly demonstrate that the overall anisotropy in these sedimentary rocks is dominated by the average pore fabric shape and orientation. Hence, the analysis of this fabric provides a good indicator of the anisotropy of other related physical properties, such as mechanical strength.
Effects of Interfacial Translation-rotation Coupling for Confined Ferrofluids
NASA Astrophysics Data System (ADS)
Fang, Angbo
2011-03-01
Ferrofluids have wide applications ranging from semiconductor fabrications to biomedical processes. The hydrodynamic spin diffusion theory for ferrofluids has been successful in explaining many experimental data, but it suffers from some fatal flaws. For example, it fails to predict the incorrect flow direction for a ferrofluid confined in a concentric cylinder channel in the presence of a rotating magnetic field. In this work we develop a method to establish the general hydrodynamic boundary conditions (BCs) for micro-polar fluids such as ferrofluids. Through a dynamic generalization of the mesoscopic diffuse interface model, we are able to obtain the surface dissipation functional, in which the interfacial translation-rotation coupling plays a significant role. The generalized hydrodynamic BCs can be obtained straightforwardly by using Onsager's variational approach. The resulted velocity profile and other quantities compares well with the experimental data, strikingly different from traditional theories. The methodology can be applied to study the hydrodynamic behavior of other structured fluids in confined channels or multi-phase flows. The work is supported by a research award made by the King Abdullah University of Science and Technology.
Hydrodynamics of the double-wave structure of insect spermatozoa flagella
Lauga, Eric
Hydrodynamics of the double-wave structure of insect spermatozoa flagella On Shun Pak, Saverio E flagellar waves, insect sperm flagella have also been observed to display a double-wave structure by propa- gating travelling waves along one or many slender flagella [4]. The motility features
Observing the Rosensweig instability of a quantum ferrofluid
Kadau, Holger; Wenzel, Matthias; Wink, Clarissa; Maier, Thomas; Ferrier-Barbut, Igor; Pfau, Tilman
2015-01-01
Ferrofluids show unusual hydrodynamic effects due to the magnetic nature of their constituents. For increasing magnetization a classical ferrofluid undergoes a Rosensweig instability and creates self-organized ordered surface structures or droplet crystals. A Bose-Einstein condensate with strong dipolar interactions is a quantum ferrofluid that also shows superfluidity. The field of dipolar quantum gases is motivated by the search for new phases that break continuous symmetries. The simultaneous breaking of continuous symmetries like the phase invariance for the superfluid state and the translational symmetry for a crystal provides the basis of novel states of matter. However, interaction-induced crystallization in a superfluid has not been observed. Here we use in situ imaging to directly observe the spontaneous transition from an unstructured superfluid to an ordered arrangement of droplets in an atomic dysprosium Bose-Einstein condensate. By utilizing a Feshbach resonance to control the interparticle inter...
Flow control using ferrofluids
NASA Astrophysics Data System (ADS)
Cornat, Francois; Beck, David; Jacobi, Ian; Stone, Howard
2013-11-01
A novel flow control technique is proposed which employs a ferrofluidic lubricant infused in a micro-patterned substrate as a ``morphing surface'' for control of wall-bounded flows. Traditionally, morphing surfaces produce dynamic changes in the curvature and roughness of solid substrates for active control of high Reynolds number flow features such as boundary layer separation and turbulent streaks. We show how these surface modifications can be achieved with a thin liquid layer in the presence of a normal magnetic field. By impregnating a chemically-treated, micro-patterned surface with a fluorinated ferrofluid, the fluid is maintained as a thin super-hydrophobic film and can be redistributed on the substrate by magnetic forces to dynamically reveal or conceal the underlying surface roughness. Moreover, the surface topography of the ferrofluid film itself can be modified to produce an enhanced roughness, beyond the scale of the underlying substrate pattern. Both types of ferrofluidic surface modifications are studied in micro- and macro- scale channels in order to assess the feasibility of flow modification at low to moderate Reynolds numbers.
Denny, Mark
The velocities and accelerations accompanying ocean waves can impose large hydrodynamic forces with these forces (Koehl, 1984, 1986; Denny, 1988; Johnson and Koehl, 1994; Friedland and Denny, 1995) suggest that the bull kelp Nereocystis luetkeana avoids the brunt of hydrodynamic forces by `going
Falcon, Eric
2011-01-01
described by our theoretical predictions. The dispersion relation of linear waves is also measured found to depend on the magnetic field applied, contrary to the predictions based on noninteracting be analytically computed by the wave turbulence theory in nearly all fields of physics (e.g., oceanic surface
Hydrodynamic forces and surface topography: Centimeter-scale spatial variation in wave forces
Denny, Mark
Hydrodynamic forces and surface topography: Centimeter-scale spatial variation in wave forces. On the rugose rock surfaces of wave-swept shores, interactions between substratum topography and wave-induced flow may create such a spatially variable environment. Topography Numerous investigators have explored
Marques, Francisco
Symmetry Breaking Via Global Bifurcations of Modulated Rotating Waves in Hydrodynamics Jan Abshagen, the Z2 symmetry of a rotating wave that occurs in Taylor-Couette flow is broken by a global saddle rotating wave. Unexpected complexity in the bifurcation structure arises as the curves of cyclic pitchfork
Dispersion Relation and Numerical Simulation of Hydrodynamic Waves In Mar's Topside Ionosphere
NASA Astrophysics Data System (ADS)
Wang, J.-S.; Nielsen, E.
The dispersion relation for hydrodynamic waves in an ionosphere with at most a weak magnetic field shows, hydrodynamic hybrid waves may be excited in the topside iono- sphere of Mars and Venus owing to fluctuations in the solar wind pressure. The hy- brid waves result from coupling between two different hydrodynamic wave modes: the classic acoustic-gravity wave(AGW) and the newly developed background gradi- ent wave(BGW). Numerical simulations show that these waves will cause wave-like structures in the altitude profiles of the ionospheric plasma density. The wavelength and frequency are various but their prevailing values in Martian ionosphere are about 60km and 0.001-0.0001Hz, respectively. The amplitudes of the plasma density vari- ations decrease nearly exponentially with increasing altitude, and are of the same or- der of the magnitude as the uncertainty on all the previous measurements of Mar- tian ionospheric electron densities. Radio occultation observations at Mars and Venus show electron density fluctuations in the high altitude ionosphere. The fluctuations are mainly noise, but they may in part be caused by hydrodynamic wave activity. To verify wave activity more detailed measurements are required, and may be obtained with the low frequency radar planned for the Mars Express mission.
Hydrodynamics of the double-wave structure of insect spermatozoa flagella
Pak, On Shun; Lauga, Eric; 10.1098/rsif.2011.0841
2012-01-01
In addition to conventional planar and helical flagellar waves, insect sperm flagella have also been observed to display a double-wave structure characterized by the presence of two superimposed helical waves. In this paper, we present a hydrodynamic investigation of the locomotion of insect spermatozoa exhibiting the double-wave structure, idealized here as superhelical waves. Resolving the hydrodynamic interactions with a non-local slender body theory, we predict the swimming kinematics of these superhelical swimmers based on experimentally collected geometric and kinematic data. Our consideration provides insight into the relative contributions of the major and minor helical waves to swimming; namely, propulsion is due primarily to the minor wave, with negligible contribution from the major wave. We also explore the dependence of the propulsion speed on geometric and kinematic parameters, revealing counter-intuitive results, particularly for the case when the minor and major helical structures are of oppos...
Particle size analysis in ferrofluids
K. O'Grady; A. Bradbury
1983-01-01
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
Magnetorheology of ferrofluid composites
NASA Astrophysics Data System (ADS)
Popplewell, J.; Rosensweig, R. E.; Siller, J. K.
1995-08-01
Composites consisting of nonmagnetic particles with sizes in the micron range suspended in a ferrofluid constitute an inverse magnetorheological fluid. Structuring occurs in an applied magnetic field and can result in the solidification of the composite. Above a critical level of applied stress the material further transforms to a liquid state. Data confirming the existence of a solidified state are presented based on constant shear rheological measurements. Measurements of the yield stress compare favorably with predictions of theory based on the analysis of unsymmetric stresses in the unyielded, anisotropic medium.
Energy harvesting via ferrofluidic induction
NASA Astrophysics Data System (ADS)
Monroe, J. G.; Vasquez, Erick S.; Aspin, Zachary S.; Fairley, John D.; Walters, Keisha B.; Berg, Matthew J.; Thompson, Scott M.
2015-05-01
A series of experiments were conducted to investigate and characterize the concept of ferrofluidic induction - a process for generating electrical power via cyclic oscillation of ferrofluid (iron-based nanofluid) through a solenoid. Experimental parameters include: number of bias magnets, magnet spacing, solenoid core, fluid pulse frequency and ferrofluid-particle diameter. A peristaltic pump was used to cyclically drive two aqueous ferrofluids, consisting of 7-10 nm iron-oxide particles and commercially-available hydroxyl-coated magnetic beads (~800 nm), respectively. The solutions were pulsated at 3, 6, and 10 Hz through 3.2 mm internal diameter Tygon tubing. A 1000 turn copper-wire solenoid was placed around the tube 45 cm away from the pump. The experimental results indicate that the ferrofluid is capable of inducing a maximum electric potential of approximately +/- 20 ?V across the solenoid during its cyclic passage. As the frequency of the pulsating flow increased, the ferro-nanoparticle diameter increased, or the bias magnet separation decreased, the induced voltage increased. The type of solenoid core material (copper or plastic) did not have a discernible effect on induction. These results demonstrate the feasibility of ferrofluidic induction and provide insight into its dependence on fluid/flow parameters. Such fluidic/magneto-coupling can be exploited for energy harvesting and/or conversion system design for a variety of applications.
Hydrodynamic analysis of elastic floating collars in random waves
NASA Astrophysics Data System (ADS)
Bai, Xiao-dong; Zhao, Yun-peng; Dong, Guo-hai; Li, Yu-cheng
2015-06-01
As the main load-bearing component of fish cages, the floating collar supports the whole cage and undergoes large deformations. In this paper, a mathematical method is developed to study the motions and elastic deformations of elastic floating collars in random waves. The irregular wave is simulated by the random phase method and the statistical approach and Fourier transfer are applied to analyze the elastic response in both time and frequency domains. The governing equations of motions are established by Newton's second law, and the governing equations of deformations are obtained based on curved beam theory and modal superposition method. In order to validate the numerical model of the floating collar attacked by random waves, a series of physical model tests are conducted. Good relationship between numerical simulation and experimental observations is obtained. The numerical results indicate that the transfer function of out-of-plane and in-plane deformations increase with the increasing of wave frequency. In the frequency range between 0.6 Hz and 1.1 Hz, a linear relationship exists between the wave elevations and the deformations. The average phase difference between the wave elevation and out-of-plane deformation is 60° with waves leading and the phase between the wave elevation and in-plane deformation is 10° with waves lagging. In addition, the effect of fish net on the elastic response is analyzed. The results suggest that the deformation of the floating collar with fish net is a little larger than that without net.
NO EFFECT OF HYDRODYNAMIC SHOCK WAVE ON PROTEIN FUNCTIONALITY OF BEEF MUSCLE
Technology Transfer Automated Retrieval System (TEKTRAN)
The protein functionality of meat proteins after treatment with hydrodynamic shock wave was determined. Frankfurters (cooked to 71 deg C) were evaluated for cooking yield, CIE L*a*b*, nitrosylhemochrome, Texture Profile Analysis (hardness, cohesiveness), and stress and strain (torsion testing). Comp...
Technology Transfer Automated Retrieval System (TEKTRAN)
Longissimus lumborum samples were removed 24 h postmortem from six U.S. Utility carcasses to be utilized in determining the effects of tenderness enhancement methods and aging time on quality attributes of beef. Within each sample, sections were randomly assigned to hydrodynamic shock waves (HSW), b...
Coupling of Hydrodynamic and Wave Models: Case Study for Hurricane Floyd (1999) Hindcast
Yuji Funakoshi; Scott C. Hagen; Peter Bacopoulos
2008-01-01
This paper demonstrates a practical application of coupling a hydrodynamic model with a wave model for the calculation of storm tide elevations in the St. Johns River Northeastern Florida. Hurricane Floyd 1999 is chosen as the storm of interest due to its track which paralleled the northeast coast of Florida without making a direct landfall on the St. Johns River.
Ferrofluid Photonic Dipole Contours
NASA Astrophysics Data System (ADS)
Snyder, Michael; Frederick, Jonathan
2008-03-01
Understanding magnetic fields is important to facilitate magnetic applications in diverse fields in industry, commerce, and space exploration to name a few. Large electromagnets can move heavy loads of metal. Magnetic materials attached to credit cards allow for fast, accurate business transactions. And the Earth's magnetic field gives us the colorful auroras observed near the north and south poles. Magnetic fields are not visible, and therefore often hard to understand or characterize. This investigation describes and demonstrates a novel technique for the visualization of magnetic fields. Two ferrofluid Hele-Shaw cells have been constructed to facilitate the imaging of magnetic field lines [1,2,3,4]. We deduce that magnetically induced photonic band gap arrays similar to electrostatic liquid crystal operation are responsible for the photographed images and seek to mathematically prove the images are of exact dipole nature. We also note by comparison that our photographs are very similar to solar magnetic Heliosphere photographs.
Smoothed Particle Hydrodynamics method to study water wave breaking and runup
NASA Astrophysics Data System (ADS)
Lominé, F.; Chambon, G.; Naaim, M.; Faug, T.
2009-04-01
The problem of determining solitary waves runups is of great interest in studying coastal effects of tsunamis. A relationship between the runup and wave height, for non-breaking waves, exists in the literature (Synolakis, 1987). Nevertheless, it is difficult to predict the runup for breaking waves. Our study aims to numerically determine the runup law for breaking waves. Therefore, we developed a numerical model based on the Smoothed Particle Hydrodynamics method (SPH) in order to study the transformation of a wave propagating over a constant depth and encountering a sloping beach. SPH is a meshfree method, where all fluid quantities are carried out by points, and is very suitable for problems involving large deformations and moving interfaces. Originally developed for astrophysical problems, this numerical method proved its efficiency to simulate free surface flows. The formalism requires to consider fluid being slightly compressible and that pressure is to be evaluated from density variations through a state equation. Our SPH code has been validated with general hydrodynamic flow problems (laminar flows, dam breaking, solitary wave runup on vertical wall, ...) using experimental or theoretical results coming from literature. Depending on problem parameters (the slope of the beach, wave amplitude, water depth,...), wave breaking can be observed and runup can be determined with the use of our numerical program.
NASA Astrophysics Data System (ADS)
Hara, Tetsu; Plant, William J.
1994-05-01
In this paper we use results of microwave backscattering experiments over the past decade to attempt to present a coherent picture of the ocean wave-radar modulation transfer function (MTF) based on composite surface theory, short-wave modulation, and modulated wind stress. A simplified relaxation model is proposed for the modulation of the gravity-capillary wavenumber spectrum by long waves. The model is based on the relaxation rate and the equilibrium gravity-capillary wavenumber spectrum. It differs from previous models by including all airflow modulation effects in the response of the equilibrium spectrum to changes in the airflow. Thus the explicit modulation of individual source functions such as wind input, short-wave dissipation, and nonlinear interactions need not be known in order to calculate the hydrodynainic MTF. By combining this new model of the hydrodynamic MTF with microwave measurements, we attempt to determine wind shear stress modulation caused by the long waves. In order to extract the hydrodynamic MTF from the microwave data, we remove tilt and range change effects from the measured MTFs using the published analytical forms for these effects. Our results show that the inferred hydrodynamic MTF is higher for II polarization scattering than for V polarization. Since this is impossible if we have obtained the true hydrodynamic MTF, these results strongly indicate a problem with composite scattering theory as it has been traditionally applied. One explanation for this result may be the effects of intermediate-scale waves suggested by Romeiser et al. (1993). Since these effects are much stronger for H polarization than for V polarization, they may explain our observed discrepancy and, if so, imply that V polarization return should yield an acceptable upper limit for the true hydrodynamic MTF. Thus we incorporate our V polarization results into the proposed model to estimate an upper limit for the wind shear stress modulation along the long-wave profile. We infer that the primary source of modulation of Bragg resonant waves depends strongly on Bragg wavenumber and windspeed. For low values of these quantities, straining by long-wave orbital velocities dominates the modulation process, while for higher values modulated wind stress becomes increasingly important. Our calculations indicate that wind stress modulation dominates the process for 3 cm Bragg waves at moderate to high wind speeds.
A Dynamic Analysis of Hydrodynamic Wave Journal Bearings
NASA Technical Reports Server (NTRS)
Ene, Nicoleta M.; Dimofte, Florin; Keith, Theo G.
2008-01-01
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.
Hydrodynamic instabilities in supernova remnants - Self-similar driven waves
NASA Technical Reports Server (NTRS)
Chevalier, Roger A.; Blondin, John M.; Emmering, Robert T.
1992-01-01
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.
Tunable optical and magneto-optical properties of ferrofluid in the terahertz regime.
Chen, Sai; Fan, Fei; Chang, Shengjiang; Miao, Yinping; Chen, Meng; Li, Jining; Wang, Xianghui; Lin, Lie
2014-03-24
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
The hydrodynamics of a wave-power device in a tapered harbor
Gallachoir, B.P.O.; Thomas, G.P. [University College, Cork (Ireland). Dept. of Mathematical Physics; Sarmento, A.J.N.A. [Instituto Superior Tecnico, Lisbon (Portugal). Dept. de Engenharia Mecanica
1995-12-31
This paper considers the hydrodynamic performance of a single wave-power device placed at the end of a tapered harbor and set in a reflecting coastline. A relatively simple model, in which the harbor width is assumed to be much smaller than the incident wavelength, is used to calculate approximate values for the hydrodynamic coefficients and hence determine the energy absorbing capabilities of the device. A comparison is presented between a device in a rectangular harbor and one in a tapered harbor in order to make a preliminary assessment of the influence of the taper.
A review of hydrodynamic investigations into arrays of ocean wave energy converters
De Chowdhury, S; Sanchez, A Madrigal; Fleming, A; Winship, B; Illesinghe, S; Toffoli, A; Babanin, A; Penesis, I; Manasseh, R
2015-01-01
Theoretical, numerical and experimental studies on arrays of ocean wave energy converter are reviewed. The importance of extracting wave power via an array as opposed to individual wave-power machines has long been established. There is ongoing interest in implementing key technologies at commercial scale owing to the recent acceleration in demand for renewable energy. To date, several reviews have been published on the science and technology of harnessing ocean-wave power. However, there have been few reviews of the extensive literature on ocean wave-power arrays. Research into the hydrodynamic modelling of ocean wave-power arrays is analysed. Where ever possible, comparisons are drawn with physical scaled experiments. Some critical knowledge gaps have been found. Specific emphasis has been paid on understanding how the modelling and scaled experiments are likely to be complementary to each other.
2DV hydrodynamics of wave–floating breakwater interaction
T. H. Koftis; P. Prinos; E. Koutandos
2006-01-01
Wave interactions with a fixed floating breakwater (FB) are investigated both numerically and experimentally. Laboratory experiments of large scale have been performed in the CIEM flume of the Catalonia University of Technology, Barcelona and measurements are compared with numerical results obtained with the use of the COBRAS model. The latter solves the two-dimensional, unsteady Reynolds averaged Navier–Stokes (RANS) equations in
NASA Astrophysics Data System (ADS)
Miike, H.; Miura, K.; Nomura, A.; Sakurai, T.
2010-06-01
We introduce a short review of chemically driven convection together with a series of our experiments on hydrodynamic instabilities induced by chemical waves excited in the batch reactor of a Belousov-Zhabotinsky reaction. Several unresolved phenomena are picked out and possible mechanisms are discussed extensively. Interesting features of these phenomena can be summarized as being caused by the ‘global and dynamic hydrodynamic pattern induced by chemical waves’. These chemically induced global pattern of hydrodynamic phenomena may not be simply explained by the reaction-diffusion-convection model based on Marangoni instability (surface tension-driven convection), which produces only a localized structure of the convection pattern. Observed flow waves show global and dynamic patterns of convection that generate a functional structure associated with hierarchical patterns appearing in the reaction-diffusion-convection system. In particular, we clarify the existence of a continuous stream of hydrodynamic flow with growing amplitude and its rotating direction. We find that the flow does not stabilize to a motionless state until the system has self-collapsed. This new picture of the flow waves requires a revision of the reaction-diffusion-convection model. The established flow structure can be regarded as a mixing and/or transport process to supply the substrate from the peripheral region to the centre of the chemical waves to sustain the reaction. This characteristic may be a function of the hierarchical structure. A new mechanism for the viscous-elastic feature of the gas-liquid interface is discussed in order to understand these curious phenomena of interest.
Quasicrystalline and Rational Approximant Wave Patterns in Hydrodynamic and Quantum Nested Wells
NASA Astrophysics Data System (ADS)
Bazán, A.; Torres, M.; Chiappe, G.; Louis, E.; Miralles, J. A.; Vergés, J. A.; Naumis, Gerardo G.; Aragón, J. L.
2006-09-01
The eigenfunctions of nested wells with an incommensurate boundary geometry, in both the hydrodynamic shallow water regime and quantum cases, are systematically and exhaustively studied in this Letter. The boundary arrangement of the nested wells consists of polygonal ones, square or hexagonal, with a concentric immersed, similar but rotated, well or plateau. A rich taxonomy of wave patterns, such as quasicrystalline states, their crystalline rational approximants, and some other exotic but well known tilings, is found in these mimicked experiments. To the best of our knowledge, these hydrodynamic rational approximants are presented here for the first time in a hydrodynamic-quantum framework. The corresponding statistical nature of the energy level spacing distribution reflects this taxonomy by changing the spectral types.
On the consistency of the drag between air and water in meteorological, hydrodynamic and wave models
NASA Astrophysics Data System (ADS)
van Nieuwkoop, Joana; Baas, Peter; Caires, Sofia; Groeneweg, Jacco
2015-07-01
For the design, assessment and flood control of water defences, hydraulic loads in terms of water levels and wave conditions are required and often obtained from numerical models. For these hydraulic loads to be reliable, accurate atmospheric forcing is required. Waves and surges are typically forced by surface stress. However, in most cases, the input for these models consists of 10-m wind velocities that are internally converted to surface stress by applying a particular drag relation. This procedure generally leads to inconsistencies, since the hydrodynamic, wave and atmospheric models often apply different drag relations. By means of a case study, we explored the consequences of this inconsistency in the drag formulation for a North Sea storm wave and surge hindcast. This was done by forcing the hydrodynamic and wave models using both the 10-m wind velocity and the surface stress fields computed by the atmospheric model. Our study results show significant differences between the wave parameter values and water levels computed with surface stress input and 10-m wind velocity input. Our goal is not to assess different drag parameterizations but to raise awareness for this issue and to plea for the use of a consistent drag relation in meteorological and hydrodynamic/wave models. The consistent use of one drag formulation facilitates the identification of problems and the eventual improvement of the drag formulation. Furthermore, we suggest using the so-called pseudo-wind, which is a translation of the surface stress to the 10-m wind speed using a reference drag relation.
Hydrodynamic sensing and behavior by oyster larvae in turbulence and waves.
Fuchs, Heidi L; Gerbi, Gregory P; Hunter, Elias J; Christman, Adam J; Diez, F Javier
2015-05-01
Hydrodynamic signals from turbulence and waves may provide marine invertebrate larvae with behavioral cues that affect the pathways and energetic costs of larval delivery to adult habitats. Oysters (Crassostrea virginica) live in sheltered estuaries with strong turbulence and small waves, but their larvae can be transported into coastal waters with large waves. These contrasting environments have different ranges of hydrodynamic signals, because turbulence generally produces higher spatial velocity gradients, whereas waves can produce higher temporal velocity gradients. To understand how physical processes affect oyster larval behavior, transport and energetics, we exposed larvae to different combinations of turbulence and waves in flow tanks with (1) wavy turbulence, (2) a seiche and (3) rectilinear accelerations. We quantified behavioral responses of individual larvae to local instantaneous flows using two-phase, infrared particle-image velocimetry. Both high dissipation rates and high wave-generated accelerations induced most larvae to swim faster upward. High dissipation rates also induced some rapid, active dives, whereas high accelerations induced only weak active dives. In both turbulence and waves, faster swimming and active diving were achieved through an increase in propulsive force and power output that would carry a high energetic cost. Swimming costs could be offset if larvae reaching surface waters had a higher probability of being transported shoreward by Stokes drift, whereas diving costs could be offset by enhanced settlement or predator avoidance. These complex behaviors suggest that larvae integrate multiple hydrodynamic signals to manage dispersal tradeoffs, spending more energy to raise the probability of successful transport to suitable locations. PMID:25788721
Symmetry Breaking Via Global Bifurcations of Modulated Rotating Waves in Hydrodynamics
Jan Abshagen; Juan M. Lopez; Francisco Marques; Gerd Pfister
2005-01-01
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
Pu, Jaan Hui; Shao, SongDong
2012-01-01
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
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
Microwave properties of ferrofluid composites
NASA Astrophysics Data System (ADS)
Popplewell, J.; Davies, P.; Llewellyn, J. P.; O'Grady, K.
1986-02-01
Ferrofluid composites containing dispersed metallic particles of tin or copper have a magnetically induced dichroism, which is particle concentration dependent, in the 3 mm microwave region. The system relaxes when the magnetic field (? 50 Oe) is removed with an initial relaxation time ??1 s. The subsequent relaxation through Brownian motion is significantly longer with ??10 3 s.
Neutron scattering studies of ferrofluids
NASA Astrophysics Data System (ADS)
Cebula, D. J.; Charles, S. W.; Popplewell, J.
1983-11-01
Neutron small angle scattering has been used to determine the structure of a ferrofluid composed of cobalt particles stabilised by a surfactant dispersed in toluene. Results obtained confirm the particle's size and the extent of the surfactant layer. The toluene carrier is shown to penetrate the adsorbed layer.
NASA Astrophysics Data System (ADS)
Freytag, B.
2015-08-01
In the Sun, low-amplitude small-scale acoustic waves are just detectable in the photosphere and start to become dynamically relevant only in the lower chromosphere. The generation of these waves by non-stationary convective flows can be studied in detail by local 3-D radiation-hydrodynamics simulations. Using this technique for global models of AGB stars reveals roughly similar phenomena but on a larger scale and with much higher amplitude. Convection cells spanning a significant fraction of the entire surface produce strong waves that cause a network of smaller shocks in the inner photosphere and occasional global shocks, travelling outward in large arcs. Material falling back interacts with the surface convection cells. A new generation of 3-D RHD simulations of these layers with CO5BOLD is presented and analyzed with particular attention given to acoustic waves and shock fronts.
Hydrodynamic instabilities and transverse waves in propagation mechanism of gaseous detonations
NASA Astrophysics Data System (ADS)
Mahmoudi, Y.; Mazaheri, K.; Parvar, S.
2013-10-01
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.
Fabrication of Multi-layered Shock Wave Tube for Hydrodynamic Instability Experiment
NASA Astrophysics Data System (ADS)
Zhu, Xiurong; Zhou, Bin; Xu, Xiang; Zhong, Yanhong; Du, Ai; Li, Yunong; Zhang, Zhihua; Shen, Jun; Wu, Guangming; Ni, Xingyuan
2011-12-01
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.
A Stability Analysis for a Hydrodynamic Three-Wave Journal Bearing
NASA Technical Reports Server (NTRS)
Ene, Nicoleta M.; Dimofte, Florin; Keith, Theo G., Jr.
2007-01-01
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.
NASA Astrophysics Data System (ADS)
Brumley, Douglas R.; Polin, Marco; Pedley, Timothy J.; Goldstein, Raymond E.
2012-12-01
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.
S. R. Massel; T. J. Done
1993-01-01
Cyclone waves directly affect the density, structure and local distribution of coral assemblages by acting as agents of mortality and colony transport. Using the meteorological record, hydrodynamic formulations and risk analysis, we predict some demographic consequences of cyclones for massive corals growing in different regions of the Great Barrier Reef. Analysis of shear, compression and tension forces generated by waves
East Frisian Wadden Sea hydrodynamics and wave effects in an unstructured-grid model
NASA Astrophysics Data System (ADS)
Grashorn, Sebastian; Lettmann, Karsten A.; Wolff, Jörg-Olaf; Badewien, Thomas H.; Stanev, Emil V.
2015-03-01
An unstructured-grid model (FVCOM) coupled to a surface wave model (FVCOM-SWAVE) with two different setups is used to investigate the hydrodynamic and wave energy conditions during a moderate wind and a storm situation in the southern North Sea. One setup covers the whole North Sea with moderately increased grid resolution at the coast, whereas the other is a very high-resolution Wadden Sea setup that is one-way coupled to the coarser North Sea model. The results of both model setups are validated, compared to each other and analysed with a focus on longshore currents and wave energy. The numerical results show that during storm conditions, strong wave-induced longshore currents occur in front of the East Frisian Wadden Sea islands with current speeds up to 1 m/s. The model setup with the higher resolution around the islands shows even stronger currents than the coarser setup. The wave-current interaction also influences the surface elevation by raising the water level in the tidal basins. The calculated wave energies show large differences between moderate wind and storm conditions with time-averaged values up to 200 kW/m.
Study of audio speakers containing ferrofluid.
Rosensweig, R E; Hirota, Y; Tsuda, S; Raj, K
2008-05-21
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. PMID:21694276
Transition to turbulence in Taylor-Couette ferrofluidic flow
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-01-01
It is known that in classical fluids turbulence typically occurs at high Reynolds numbers. But can turbulence occur at low Reynolds numbers? Here we investigate the transition to turbulence in the classic Taylor-Couette system in which the rotating fluids are manufactured ferrofluids with magnetized nanoparticles embedded in liquid carriers. We find that, in the presence of a magnetic field transverse to the symmetry axis of the system, turbulence can occur at Reynolds numbers that are at least one order of magnitude smaller than those in conventional fluids. This is established by extensive computational ferrohydrodynamics through a detailed investigation of transitions in the flow structure, and characterization of behaviors of physical quantities such as the energy, the wave number, and the angular momentum through the bifurcations. A finding is that, as the magnetic field is increased, onset of turbulence can be determined accurately and reliably. Our results imply that experimental investigation of turbulence may be feasible by using ferrofluids. Our study of transition to and evolution of turbulence in the Taylor-Couette ferrofluidic flow system provides insights into the challenging problem of turbulence control. PMID:26065572
Transition to turbulence in Taylor-Couette ferrofluidic flow.
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-01-01
It is known that in classical fluids turbulence typically occurs at high Reynolds numbers. But can turbulence occur at low Reynolds numbers? Here we investigate the transition to turbulence in the classic Taylor-Couette system in which the rotating fluids are manufactured ferrofluids with magnetized nanoparticles embedded in liquid carriers. We find that, in the presence of a magnetic field transverse to the symmetry axis of the system, turbulence can occur at Reynolds numbers that are at least one order of magnitude smaller than those in conventional fluids. This is established by extensive computational ferrohydrodynamics through a detailed investigation of transitions in the flow structure, and characterization of behaviors of physical quantities such as the energy, the wave number, and the angular momentum through the bifurcations. A finding is that, as the magnetic field is increased, onset of turbulence can be determined accurately and reliably. Our results imply that experimental investigation of turbulence may be feasible by using ferrofluids. Our study of transition to and evolution of turbulence in the Taylor-Couette ferrofluidic flow system provides insights into the challenging problem of turbulence control. PMID:26065572
Metachronal waves in the flagellar beating of Volvox and their hydrodynamic origin
Brumley, Douglas R.; Polin, Marco; Pedley, Timothy J.; Goldstein, Raymond E.
2015-01-01
Groups of eukaryotic cilia and flagella are capable of coordinating their beating over large scales, routinely exhibiting collective dynamics in the form of metachronal waves. The origin of this behaviour—possibly influenced by both mechanical interactions and direct biological regulation—is poorly understood, in large part due to a lack of quantitative experimental studies. Here we characterize in detail flagellar coordination on the surface of the multicellular alga Volvox carteri, an emerging model organism for flagellar dynamics. Our studies reveal for the first time that the average metachronal coordination observed is punctuated by periodic phase defects during which synchrony is partial and limited to specific groups of cells. A minimal model of hydrodynamically coupled oscillators can reproduce semi-quantitatively the characteristics of the average metachronal dynamics, and the emergence of defects. We systematically study the model's behaviour by assessing the effect of changing intrinsic rotor characteristics, including oscillator stiffness and the nature of their internal driving force, as well as their geometric properties and spatial arrangement. Our results suggest that metachronal coordination follows from deformations in the oscillators' limit cycles induced by hydrodynamic stresses, and that defects result from sufficiently steep local biases in the oscillators' intrinsic frequencies. Additionally, we find that random variations in the intrinsic rotor frequencies increase the robustness of the average properties of the emergent metachronal waves. PMID:26040592
Metachronal waves in the flagellar beating of $Volvox$ and their hydrodynamic origin
Douglas R. Brumley; Marco Polin; Timothy J. Pedley; Raymond E. Goldstein
2015-05-10
Groups of eukaryotic cilia and flagella are capable of coordinating their beating over large scales, routinely exhibiting collective dynamics in the form of metachronal waves. The origin of this behaviour -- possibly influenced by both mechanical interactions and direct biological regulation -- is poorly understood, in large part due to lack of quantitative experimental studies. Here we characterise in detail flagellar coordination on the surface of the multicellular alga $Volvox~carteri$, an emerging model organism for flagellar dynamics. Our studies reveal for the first time that the average metachronal coordination observed is punctuated by periodic phase defects during which synchrony is partial and limited to specific groups of cells. A minimal model of hydrodynamically coupled oscillators can reproduce semi-quantitatively the characteristics of the average metachronal dynamics, and the emergence of defects. We systematically study the model's behaviour by assessing the effect of changing intrinsic rotor characteristics, including oscillator stiffness and the nature of their internal driving force, as well as their geometric properties and spatial arrangement. Our results suggest that metachronal coordination follows from deformations in the oscillators' limit cycles induced by hydrodynamic stresses, and that defects result from sufficiently steep local biases in the oscillators' intrinsic frequencies. Additionally, we find that random variations in the intrinsic rotor frequencies increase the robustness of the average properties of the emergent metachronal waves.
Metachronal waves in the flagellar beating of Volvox and their hydrodynamic origin.
Brumley, Douglas R; Polin, Marco; Pedley, Timothy J; Goldstein, Raymond E
2015-07-01
Groups of eukaryotic cilia and flagella are capable of coordinating their beating over large scales, routinely exhibiting collective dynamics in the form of metachronal waves. The origin of this behavior--possibly influenced by both mechanical interactions and direct biological regulation--is poorly understood, in large part due to a lack of quantitative experimental studies. Here we characterize in detail flagellar coordination on the surface of the multicellular alga Volvox carteri, an emerging model organism for flagellar dynamics. Our studies reveal for the first time that the average metachronal coordination observed is punctuated by periodic phase defects during which synchrony is partial and limited to specific groups of cells. A minimal model of hydrodynamically coupled oscillators can reproduce semi-quantitatively the characteristics of the average metachronal dynamics, and the emergence of defects. We systematically study the model's behaviour by assessing the effect of changing intrinsic rotor characteristics, including oscillator stiffness and the nature of their internal driving force, as well as their geometric properties and spatial arrangement. Our results suggest that metachronal coordination follows from deformations in the oscillators' limit cycles induced by hydrodynamic stresses, and that defects result from sufficiently steep local biases in the oscillators' intrinsic frequencies. Additionally, we find that random variations in the intrinsic rotor frequencies increase the robustness of the average properties of the emergent metachronal waves. PMID:26040592
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
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.
NASA Astrophysics Data System (ADS)
Griv, Evgeny; Wang, Hsiang-Hsu
2014-07-01
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.
NASA Astrophysics Data System (ADS)
Lasky, Paul D.; Bennett, Mark F.; Melatos, Andrew
2013-03-01
Hydrodynamic turbulence driven by crust-core differential rotation imposes a fundamental noise floor on gravitational wave observations of neutron stars. The gravitational wave emission peaks at the Kolmogorov decoherence frequency which, for reasonable values of the crust-core shear, ??, occurs near the most sensitive part of the frequency band for ground-based, long-baseline interferometers. We calculate the energy density spectrum of the stochastic gravitational wave background from a cosmological population of turbulent neutron stars generalizing previous calculations for individual sources. The spectrum resembles a piecewise power law, ?gw(?)=????, with ?=-1 and 7 above and below the decoherence frequency respectively, and its normalization scales as ???(??)7. Nondetection of a stochastic signal by Initial LIGO implies an upper limit on ?? and hence by implication on the internal relaxation time scale for the crust and core to come into corotation, ?d=??/??, where ?? is the observed electromagnetic spin-down rate, with ?d?107yr for accreting millisecond pulsars and ?d?105yr for radio-loud pulsars. Target limits on ?d are also estimated for future detectors, namely Advanced LIGO and the Einstein Telescope, and are found to be astrophysically interesting.
NASA Astrophysics Data System (ADS)
Marques, Wilson, Jr.; Jacinta Soares, Ana; Pandolfi Bianchi, Miriam; Kremer, Gilberto M.
2015-06-01
A shock wave structure problem, like the one which can be formulated for the planar detonation wave, is analyzed here for a binary mixture of ideal gases undergoing the symmetric reaction {{A}1}+{{A}1}\\rightleftharpoons {{A}2}+{{A}2}. The problem is studied at the hydrodynamic Euler limit of a kinetic model of the reactive Boltzmann equation. The chemical rate law is deduced in this frame with a second-order reaction rate, in a chemical regime such that the gas flow is not far away from the chemical equilibrium. The caloric and the thermal equations of state for the specific internal energy and temperature are employed to close the system of balance laws. With respect to other approaches known in the kinetic literature for detonation problems with a reversible reaction, this paper aims to improve some aspects of the wave solution. Within the mathematical analysis of the detonation model, the equation of the equilibrium Hugoniot curve of the final states is explicitly derived for the first time and used to define the correct location of the equilibrium Chapman–Jouguet point in the Hugoniot diagram. The parametric space is widened to investigate the response of the detonation solution to the activation energy of the chemical reaction. Finally, the mathematical formulation of the linear stability problem is given for the wave detonation structure via a normal-mode approach, when bidimensional disturbances perturb the steady solution. The stability equations with their boundary conditions and the radiation condition of the considered model are explicitly derived for small transversal deviations of the shock wave location. The paper shows how a second-order chemical kinetics description, derived at the microscopic level, and an analytic deduction of the equilibrium Hugoniot curve, lead to an accurate picture of the steady detonation with reversible reaction, as well as to a proper bidimensional linear stability analysis.
From AdS/CFT correspondence to hydrodynamics. II. Sound waves
G. Policastro; D. T. Son; A. O. Starinets
2005-07-26
As a non-trivial check of the non-supersymmetric gauge/gravity duality, we use a near-extremal black brane background to compute the retarded Green's functions of the stress-energy tensor in N=4 super-Yang-Mills (SYM) theory at finite temperature. For the long-distance, low-frequency modes of the diagonal components of the stress-energy tensor, hydrodynamics predicts the existence of a pole in the correlators corresponding to propagation of sound waves in the N=4 SYM plasma. The retarded Green's functions obtained from gravity do indeed exhibit this pole, with the correct values for the sound speed and the rate of attenuation.
Small, medium and large shock waves for non-equilibrium radiation hydrodynamic
Corrado Mascia
2012-02-13
We examine the existence of shock profiles for a hyperbolic-elliptic system arising in radiation hydrodynamics. The algebraic-differential system for the wave profile is reduced to a standard two-dimensional form that is analyzed in details showing the existence of heteroclinic connection between the two singular points of the system for any distance between the corresponding asymptotic states of the original model. Depending on the location of these asymptotic states, the profile can be either continuous or possesses at most one point of discontinuity. Moreover, a sharp threshold relative to presence of an internal absolute maximum in the temperature profile --also called {\\sf Zel'dovich spike}-- is rigourously derived.
Controlling ferrofluid permeability across the blood-brain barrier model
NASA Astrophysics Data System (ADS)
Shi, Di; Sun, Linlin; Mi, Gujie; Sheikh, Lubna; Bhattacharya, Soumya; Nayar, Suprabha; Webster, Thomas J.
2014-02-01
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 FITC-Dextran 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).
Anisotropic Light Scattering from Ferrofluids
NASA Astrophysics Data System (ADS)
Rablau, Corneliu; Vaishnava, Prem; Naik, Ratna; Lawes, Gavin; Tackett, Ron; Sudakar, C.
2008-03-01
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).
Rheological Properties of Iron Oxide Based Ferrofluids
NASA Astrophysics Data System (ADS)
Devi, M.; Mohanta, D.
2009-06-01
In the present work, we report synthesis and magneto-viscous properties of cationic and anionic surfactant coated, iron oxide nanoparticles based ferrofluids. Structural and morphological aspects are revealed by x-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. We compare the rheological/magneto-viscous properties of different ferrofluids for various shear rates (2-450 sec-1) and applied magnetic fields (0-100 gauss). In the absence of a magnetic field, and under no shear case, the ferrofluid prepared with TMAH coated particle is found to be 12% more viscous compared to its counterpart. The rheological properties are governed by non-Newtonian features, and for a definite shear rate, viscosity of a given ferrofluid is found to be strongly dependent on the applied magnetic field as well as nature of the surfactant.
The Effect of Morphology, Tides and Wind Waves on the Hydrodynamics of Idealized River-Mouth Systems
NASA Astrophysics Data System (ADS)
Olabarrieta, M.; Coco, G.; Zhou, Z.
2012-12-01
The hydrodynamics and the morphological configuration of estuaries strongly depend on tidal wave propagation, offshore wave climate, and river discharges. Depending of their relative contribution, an estuary can exhibit a wave-dominated morphology, a tidal-dominated configuration, or a river dominated one. This has a direct effect on hydrodynamic parameters relevant from the ecological and biological points of view. Overall, these coastal systems are highly dynamic and complex and the interplay of the physical processes and the resulting dynamics are still not fully understood. The 3D COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) modeling system is applied to analyze numerically wave-tidal hydrodynamics in 3 idealized inlet-estuary configurations. The configurations differ because of the presence/absence of the ebb delta and a main channel crossing the delta and because of the water depths inside the estuary. In essence we consider different wave climates, tidal prisms, and standing/progressive tidal conditions. The goal is to infer the effect of the ebb delta on the combined wave-tidal flows along a whole tidal cycle and its dependency with the characteristics of the tides and the incoming swell waves. The interaction between surface gravity waves and currents is modeled with the 3D vortex force method, which decouples conservative and non-conservative wave forces. We show how the ebb shoal acts as a roughness element increasing energy losses in the inlet area. It also enhances the relative effect of the wave driven forces and circulations in the inlet region. The effect of waves is not confined to the inlet and its influence extends to the inner part of the estuary. These are manifested on increased mean water levels, dissipation of the main tidal harmonics and a more progressive character of the tides inside the estuary. The main forces responsible for these changes are wave breaking induced accelerations and the increase of bed friction. Tidal modulations of the full directional wave spectra are also identified in the inlet region. The wave penetration capacity into the estuary changes during a tidal cycle, because of variations in the energy dissipation over the ebb shoal and because the wave action advection by the tidal currents. The momentum balance analysis performed along the whole tidal cycle shows tidal modulations of the wave induced forces as a consequence of temporal and spatial variations in water depths and tidal currents. This presentation will discuss the relevance of the wave induced forces on the inlet estuarine systems pointing out the limitations and future efforts in these directions.
Visualizing Magnetism with Optical Ferrofluid Cells
NASA Astrophysics Data System (ADS)
Snyder, Michael
2015-05-01
a novel technique for the visualization of magnetic fields. The ferrofluid cells are made up of two optically flat windows with a layer of Fe3O4/Fe2O3 ferrofluid between the glass. Using different magnet configurations and lighting, highly structured pictures are obtained of one of the universes forces. Characterized as the magneto-optic Kerr/displacement current effect on self assembled micrometer sized helical rods of Fe304/Fe203.
Magnetic detection of ferrofluid injection zones
Borglin, S.; Moridis, G.; Becker, A.
1998-03-01
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.
NASA Astrophysics Data System (ADS)
Ganju, N. K.; Sherwood, C. R.; Signell, R. P.
2008-12-01
Sorted grain-size features, also known as rippled scour depressions, are persistent cross-shore structures found in many nearshore environments, characterized by sharp gradients in grain size and gentle relief in the alongshore direction. The formation of these features is not completely understood, but self-organization and feedback have been proposed as explanations for their persistence. Sorted grain-size features near the Martha's Vineyard Coastal Observatory (MVCO), Massachusetts, are characterized by bathymetric lows with coarse (0.5 mm) sand and large ripples (heights of 0.10-0.15 cm, wavelengths of 0.6 to 0.8 m) and bathymetric highs with fine sand (0.125 mm) and small ripples (heights of 0.01 m, wavelengths of 0.1 m). The features extend from the shallowest region surveyed (6 m) to depths of 17 m, 3 km offshore, with a maximum alongshore width of less than 1 km. Wave-current interaction is an important component of the inner shelf and circulation at MVCO. However, subtle changes in topography and hydrodynamic roughness associated with these features complicate evaluation of numerical models, especially because of the spatial and temporal variability in alongshore flows and wave forcing near MVCO. We have investigated these features and the inner-shelf circulation using nested and coupled wave-hydrodynamic models. The models were calibrated using water-level, current, and wave data from MVCO and several wave buoys. The suite of nested models applied here began with basin- scale (5-km grid for the eastern seaboard) wave models that provided spectral wave forcing to a regional wave model (1-km grid for the southern New England shelf). The regional wave model and a regional hydrodynamic model at the same scale were then run uncoupled, to provide boundary conditions for a cascade of nested, coupled, wave-hydrodynamic models. The final nested model, at an 8-m grid resolution, resolved the sorted grain-size features. At this level, a sediment-transport model with time-dependent ripple geometry and various roughness formulations was applied to investigate the maintenance of these features and their influence on circulation under realistic conditions. Given an initial bed sediment distribution, the roughness introduced by these features significantly alters the quasi-steady-state distribution within the bed, and highlights the concept of feedback and self-organization.
NASA Astrophysics Data System (ADS)
Smith, Kevin; Paterson, Eric
2008-11-01
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.
NASA Astrophysics Data System (ADS)
Larecki, Wieslaw; Banach, Zbigniew
2010-09-01
Various phenomenological theories of wave-type heat transport, which can be interpreted as the models of an isotropic rigid heat conductor with an internal vector state variable, have been proposed in the literature with the objective to describe the second sound propagation in dielectric crystals. The aim of this paper is to analyze the relation between these phenomenological approaches and the phonon gas hydrodynamics. The four-moment phonon gas hydrodynamics based on the maximum entropy closure of the moment equations with nonlinear isotropic phonon dispersion relation is considered for this purpose. We reformulate the equations of this hydrodynamics in terms of energy and quasi-momentum as the primitive fields and subsequently demonstrate that, from the macroscopic point of view, they can be understood as describing the reference model of an isotropic rigid heat conductor with quasi-momentum playing the role of the internal vector state variable. This model is determined by the entropy function and the additional scalar potential, but if the finite domain of phonon wave vectors is approximated by the whole space, the additional potential can be expressed in terms of the entropy function and its first derivatives. Then the transformation of primitive fields and the expansion of thermodynamic potentials in powers of the square of quasi-momentum enable us to compare the reference model with the models proposed earlier in the literature. It is shown that the previous models require some subtle modifications in order to achieve full consistency with phonon gas hydrodynamics.
A contribution about ferrofluid based flow manipulation and locomotion systems
NASA Astrophysics Data System (ADS)
Zimmermann, K.; Zeidis, I.; Bohm, V.; Popp, J.
2009-02-01
With the background of developing apedal bionic inspired locomotion systems for future application fields like autonomous (swarm) robots, medical engineering and inspection systems, this article presents a selection of locomotion systems with bifluidic flow control using ferrofluid. By controlling the change of shape, position and pressure of the ferrofluid in a secondary low viscous fluid by magnetic fields locomotion of objects or the ferrofluid itself can be realised. The locomotion of an object is caused in the first example by a ferrofluid generated flow of the secondary fluid and in the second and third case by the direct alteration of the ferrofluid position.
NASA Astrophysics Data System (ADS)
Chen, Jia-Lin; Hsu, Tian-Jian; Shi, Fengyan; Raubenheimer, Britt; Elgar, Steve
2015-06-01
The interactions between waves, tidal currents, and bathymetry near New River Inlet, NC, USA are investigated to understand the effects on the resulting hydrodynamics and sediment transport. A quasi-3-D nearshore community model, NearCoM-TVD, is used in this integrated observational and modeling study. The model is validated with observations of waves and currents at 30 locations, including in a recently dredged navigation channel and a shallower channel, and on the ebb tidal delta, for a range of flow and offshore wave conditions during May 2012. In the channels, model skills for flow velocity and wave height are high. Near the ebb tidal delta, the model reproduces the observed rapid onshore (offshore) decay of wave heights (current velocities). Model results reveal that this sharp transition coincides with the location of the breaker zone over the ebb tidal delta, which is modulated by semidiurnal tides and by wave intensity. The modulation of wave heights is primarily owing to depth changes rather than direct wave-current interaction. The modeled tidally averaged residual flow patterns show that waves play an important role in generating vortices and landward-directed currents near the inlet entrance. Numerical experiments suggest that these flow patterns are associated with the channel-shoal bathymetry near the inlet, similar to the generation of rip currents. Consistent with other inlet studies, model results suggest that tidal currents drive sediment fluxes in the channels, but that sediment fluxes on the ebb tidal delta are driven primarily by waves.
Falling ball viscometry of magnetized ferrofluids
NASA Astrophysics Data System (ADS)
Cali, Alex; Lee, W. K.; Nunez, Samuel, Jr.; Prescod, Joy; Smith, Rose; Trubatch, A. D.; Vieira, Matthew; Yecko, Philip
2011-11-01
Falling spheres of 500 ?m were used to perform viscometric experiments on magnetized ferrofluids. The role of the angle of orientation of an applied unifom field relative to the direction of fall has been examined with high speed phase contrast imaging using the Advanced Photon Source. The magnetized ferrofluid exhibits an anisotropic viscosity that we can quantify in terms of a tensorial viscosity coefficient. We find that the effective drag is greater when the fall occurs normal to the applied field rather than parallel to it, a result that is opposite to what is predicted by many ferrofluid magnetoviscosity models, but consistent with the properties of electro- and magneto-rheological fluid, liquid crystal, and polymer fluid rheology models. Finally, we discuss the dispersion of these results in terms of thread-like aggregations of magnetic particles observed in the experiments. supported by NSF grant no. MPS-1016383
Magnetic relaxation and dissipative heating in ferrofluids
NASA Astrophysics Data System (ADS)
Vaishnava, P. P.; Tackett, R.; Dixit, A.; Sudakar, C.; Naik, R.; Lawes, G.
2007-09-01
We have investigated the ac magnetic susceptibility and magnetic heating of aqueous suspensions of ?-Fe2O3 nanoparticles embedded in alginate hydrogel matrix and isolated ?-Fe2O3 and Fe3O4 nanoparticles coated with tetramethyl ammonium hydroxide. All three ferrofluids were characterized by measuring the dc magnetization, ac susceptibility, and magnetic heating. We found that significant Néel relaxation is present in all samples, but only the isolated nanoparticle ferrofluids show any significant feature associated with Brownian relaxation near the freezing temperature of the carrier liquid. The heating rate of the ferrofluids varies systematically with the magnitude of the Brownian relaxation peak, despite similar values of the absolute magnetization. These results highlight the importance of the Brownian relaxation for heating applications incorporating magnetic nanoparticles.
Skorobogatiy, Maksim
Terahertz Faraday rotation in a magnetic liquid: High magneto-optical figure of merit and broadband) Faraday rotation in a liquid in the terahertz (THz) regime. Using a ferrofluid, a high broadband rotation of a propagating electromagnetic wave can induce linear (Voigt) or circular (Faraday) birefringence, respec- tively
Dynamics of Ferrofluidic Drops Impacting Superhydrophobic Surfaces
Bolleddula, D A; Alliseda, A; Bhosale, P; Berg, J C
2010-01-01
This is a fluid dynamics video illustrating the impact of ferrofluidic droplets on surfaces of variable wettability. Surfaces studied include mica, teflon, and superhydrophobic. A magnet is placed beneath each surface, which modifies the behavior of the ferrofluid by applying additional downward force apart from gravity resulting in reduced droplet size and increased droplet velocity. For the superhydrophobic droplet a jetting phenomena is shown which only occurs in a limited range of impact speeds, higher than observed before, followed by amplified oscillation due to magnetic field as the drop stabilizes on the surface.
NASA Astrophysics Data System (ADS)
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
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.
NASA Technical Reports Server (NTRS)
Klein, Richard I.; Mckee, Christopher F.; Colella, Philip
1994-01-01
The interstellar medium (ISM) is inhomogeneous, with clouds of various temperatures and densities embedded in a tenuous intercloud medium. Shocks propagating through the ISM can ablate or destroy the clouds, at the same time significantly altering the properties of the intercloud medium. This paper presents a comprehensive numerical study of the simplest case of the interaction between a shock wave and a spherical cloud, in which the shock far from the cloud is steady and planar, and in which radiative losses, thermal conduction, magnetic fields, and gravitational forces are all neglected. As a result, the problem is completely specified by two numbers: the Mach number of the shock, M, and the ratio of the density of the cloud to that of the intercloud medium, Chi. For strong shocks we show that the dependence on M scales out, so the primary independent parameter is Chi. Variations from this simple case are also considered: the potential effect of radiative losses is assessed by calculations in which the ratio of specific heats in the cloud is 1.1 instead of 5/3; the effect of the initial shape of the cloud is studied by using a cylindrical cloud instead of a spherical one; and the role of the initial shock is determined by considering the case of a cloud embedded in a wind. Local adaptive mesh refinement techniques with a second-order, two-fluid, two-dimensional Godunov hydrodynamic scheme are used to address these problems, allowing heretofore unobtainable numerical resolution. Convergence studies to be described in a subsequent paper demonstrate that about 100 zones per cloud radius are needed for accurate results; previous calculations have generally used about a third of this number. The results of the calculations are analyzed in terms of global quantities which provide an overall description of te shocked cloud: the size and shape of the cloud, the mean density, the mean pressure, the mean velocity, the velocity dispersion, and the total circulation.
Wave propagation algorithms on curved manifolds with applications to relativistic hydrodynamics
NASA Astrophysics Data System (ADS)
Bale, Derek Shelby
Many interesting physical systems are successfully modeled with time-dependent hyperbolic conservation laws on smooth manifolds. Examples of such systems include classical hydrodynamic flows in non-trivial geometry that are important in aerodynamic modeling, or the structure of shallow water flow on the surface of the earth important in climate modeling and oceanography. Another example arises in the study of relativistic flow of matter in the presence of compact objects like neutron stars and black holes. Astronomers wish to study this in order to understand the high-energy radiation emitted from violent relativistic events such as the formation of bi-polar jets in active galactic nuclei, the collapse of very massive stars, and gamma-ray bursts. In this dissertation, we present a new high-resolution finite volume algorithm, an extension of the wave propagation method of LeVeque, to solve hyperbolic systems of conservation laws on general manifolds, M . The representation of such equations on M introduces geometric terms due to the fact that the underlying basis will, in general, be spatially varying. For scalar components of the conservation laws, these geometric terms appear only in the flux function so that an autonomous flux function gains an explicit dependence on spatial variables through metric functions on M . We develop a general approach to handle such spatially varying flux functions in the context of wave propagation. In addition to spatially varying flux functions, vector components of the conservation laws will have geometrically induced source terms. The algorithm presented in this thesis avoids numerical complications that can arise from such source terms by treating the divergence operator in a local way. Cell averages are updated by solving modified Riemann problems. The modifications to Riemann data take care of source terms locally, thereby avoiding the need for an operator split approach for the sources. The new algorithm has been implemented in the software package CLAWMAN, a freely available set of Fortran 90 routines. The implementation is general and can be used for different systems of conservation laws on a variety of manifolds. We demonstrate that the method works well on both flat and curved manifolds by presenting examples of the algorithm and its implementation for both classical and relativistic conservation laws on various manifolds.
Lacy, J.R.; Sherwood, C.R.; Wilson, D.J.; Chisholm, T.A.; Gelfenbaum, G.R.
2005-01-01
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.
NASA Astrophysics Data System (ADS)
Bonelli, Giulio; Sciarappa, Antonio; Tanzini, Alessandro; Vasko, Petr
2014-07-01
We show that the exact partition function of U( N) six-dimensional gauge theory with eight supercharges on ?2 × S 2 provides the quantization of the integrable system of hydrodynamic type known as gl( N) periodic Intermediate Long Wave (ILW). We characterize this system as the hydrodynamic limit of elliptic Calogero-Moser integrable system. We compute the Bethe equations from the effective gauged linear sigma model on S 2 with target space the ADHM instanton moduli space, whose mirror computes the Yang-Yang function of gl( N) ILW. The quantum Hamiltonians are given by the local chiral ring observables of the six-dimensional gauge theory. As particular cases, these provide the gl( N) Benjamin-Ono and Korteweg-de Vries quantum Hamiltonians. In the four dimensional limit, we identify the local chiral ring observables with the conserved charges of Heisenberg plus W N algebrae, thus providing a gauge theoretical proof of AGT correspondence.
Ferrofluids from prism-like nanoparticles
NASA Astrophysics Data System (ADS)
Ramaye, Y.; Neveu, S.; Cabuil, V.
2005-03-01
Decomposition of iron pentacarbonyl in kerosene in the presence of octanoic acid and bis-2-ethylhexylamine leads to very monodisperse iron nanoparticles and thus to monodisperse magnetic nanoparticles. These latter can be spherical or appear as triangles on MET pictures. SAXS and AFM indicate that particles are more likely prisms. They can be dispersed in cyclohexane to produce ferrofluids.
Ferrofluidic solenoid with axial and radial displacement
NASA Technical Reports Server (NTRS)
Sabelman, E. E.
1972-01-01
New design is proposed for ferrofluidic solenoid with low magnetic flux leakage. Solenoid consists of a coil centered within a football-shaped elastomeric capsule filled with a ferromagnetic fluid. Fluid replaces the solid, movable core of conventional solenoids, and elastomeric capsule acts as return spring.
A Novel Implantable Glaucoma Valve Using Ferrofluid
Paschalis, Eleftherios I.; Chodosh, James; Sperling, Ralph A.; Salvador-Culla, Borja; Dohlman, Claes
2013-01-01
Purpose To present a novel design of an implantable glaucoma valve based on ferrofluidic nanoparticles and to compare it with a well-established FDA approved valve. Setting Massachusetts Eye & Ear Infirmary, Boston, USA. Methods A glaucoma valve was designed using soft lithography techniques utilizing a water-immiscible magnetic fluid (ferrofluid) as a pressure-sensitive barrier to aqueous flow. Two rare earth micro magnets were used to calibrate the opening and closing pressure. In-vitro flow measurements were performed to characterize the valve and to compare it to Ahmed™ glaucoma valve. The reliability and predictability of the new valve was verified by pressure/flow measurements over a period of three months and X-ray diffraction (XRD) analysis over a period of eight weeks. In vivo assessment was performed in three rabbits. Results In the in vitro experiments, the opening and closing pressures of the valve were 10 and 7 mmHg, respectively. The measured flow/pressure response was linearly proportional and reproducible over a period of three months (1.8 µl/min at 12 mmHg; 4.3 µl/min at 16 mmHg; 7.6 µl/min at 21 mmHg). X-ray diffraction analysis did not show oxidization of the ferrofluid when exposed to water or air. Preliminary in vivo results suggest that the valve is biocompatible and can control the intraocular pressure in rabbits. Conclusions The proposed valve utilizes ferrofluid as passive, tunable constriction element to provide highly predictable opening and closing pressures while maintaining ocular tone. The ferrofluid maintained its magnetic properties in the aqueous environment and provided linear flow to pressure response. Our in-vitro tests showed reliable and reproducible results over a study period of three months. Preliminary in-vivo results were very promising and currently more thorough investigation of this device is underway. PMID:23840691
Hitoshi Miura; Taishi Nakamoto
2006-11-09
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 Sekiya et al. (2003). We found that the non-linear terms in the hydrodynamical equations neglected by Sekiya et al. (2003) 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.
NASA Astrophysics Data System (ADS)
Miura, Hitoshi; Nakamoto, Taishi
2007-05-01
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.
NASA Astrophysics Data System (ADS)
Larecki, Wieslaw; Banach, Zbigniew
2014-01-01
This paper analyzes the propagation of the waves of weak discontinuity in a phonon gas described by the four-moment maximum entropy phonon hydrodynamics involving a nonlinear isotropic phonon dispersion relation. For the considered hyperbolic equations of phonon gas hydrodynamics, the eigenvalue problem is analyzed and the condition of genuine nonlinearity is discussed. The speed of the wave front propagating into the region in thermal equilibrium is first determined in terms of the integral formula dependent on the phonon dispersion relation and subsequently explicitly calculated for the Dubey dispersion-relation model: |k|=?c-1(1+b?2). The specification of the parameters c and b for sodium fluoride (NaF) and semimetallic bismuth (Bi) then makes it possible to compare the calculated dependence of the wave-front speed on the sample’s temperature with the empirical relations of Coleman and Newman (1988) describing for NaF and Bi the variation of the second-sound speed with temperature. It is demonstrated that the calculated temperature dependence of the wave-front speed resembles the empirical relation and that the parameters c and b obtained from fitting respectively the empirical relation and the original material parameters of Dubey (1973) are of the same order of magnitude, the difference being in the values of the numerical factors. It is also shown that the calculated temperature dependence is in good agreement with the predictions of Hardy and Jaswal’s theory (Hardy and Jaswal, 1971) on second-sound propagation. This suggests that the nonlinearity of a phonon dispersion relation should be taken into account in the theories aiming at the description of the wave-type phonon heat transport and that the Dubey nonlinear isotropic dispersion-relation model can be very useful for this purpose.
Anomalous attenuation of ultrasound in ferrofluids under the influence of a magnetic field
NASA Technical Reports Server (NTRS)
Isler, W. E.; Chung, D. Y.
1978-01-01
Ultrasonic wave propagation has been studied in a water-base ferrofluid by pulse-echo methods. A commercial box-car integrator was used to measure the change in attenuation due to an external magnetic field applied at various angles relative to the ultrasonic propagation vector. Anomalous results were obtained when the attenuation was plotted as a function of the magnetic field strength. As the field increased, the attenuation reached a maximum and then decreased to a flat minimum before it approached saturation at a field of 2 KG. This variation of attenuation with magnetic field cannot be explained from the simple picture derivable from the work of McTague on the viscosity of ferrofluids. In no case was the viscosity seen to decrease with field, nor was the oscillatory behavior observed. The results of this study were compared with the theory developed by Parsons.
Hydrodynamic Instabilities and Surface Waves in a Flow over an Impedance Wall
S. W. Rienstra
1986-01-01
A 2-D analysis is made of the surface waves in a subsonic compressible uni- form mean flow along an impedance wall. It is found that a raximum of four surface waves is possible. The regions of existence in complex impedance and wave number planes are given. One wave is found to travel upstream, while the others, one of which is
Andreev, P. A.; Kuzmenkov, L. S.; Trukhanova, M. I. [Department of General Physics, Physics Faculty, Moscow State University, Moscow (Russian Federation); Dpartment of Theoretical Physics, Physics Faculty, Moscow State University, Moscow (Russian Federation)
2011-12-15
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 Schroedinger equation. Fundamental QHD equations for charged and neutral particles were derived from the many-particle microscopic Schroedinger 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.
MANUEL PORTILHEIRO; ATHANASIOS E. TZAVARAS
We consider a class of kinetic equations equipped with a single conservation law which generate L1-contractions. We discuss the hydrodynamic limit to a scalar conservation law and the diffusive limit to a (possibly) degenerate parabolic equation. The limits are obtained in the \\
Microstructural investigation of some biocompatible ferrofluids
NASA Astrophysics Data System (ADS)
R?cuciu, M.; Creang?, D. E.; B?descu, V.; Sulitanu, N.
2007-09-01
Two batches of aqueous ferrofluids based on iron oxide particles as solid nanomagnetic phase have been prepared by applying the chemical precipitation method. Tetramethylammonium hydroxide (N(CH 3) 4OH) and citric acid (C 6H 8O 7) were used to functionalize magnetic cores. Physical tests have been performed in order to reveal the microstructural and magnetic features, both needed for biomedical utilization. The particle size was investigated using transmission electron microscopy (TEM), magnetization measurements and X-ray diffraction (for composition and phase information). The dimensional distribution of the ferrophase physical diameter was comparatively discussed using the box-plot statistical method revealing the fulfilling of the main requirements for ferrofluid stability.
Experimental studies of the hydrodynamic characteristics of a sloped wave energy device
Lin, Chia-Po
2000-07-19
Many wave energy convertors are designed to use either vertical (heave) or horizontal (surge) movements of waves. But the frequency response of small heaving buoys and oscillating water column devices shows that they are ...
Wave characteristic and morphologic effects on the onshore hydrodynamic response of tsunamis
Apotsos, A.; Jaffe, B.; Gelfenbaum, G.
2011-01-01
While the destruction caused by a tsunami can vary significantly owing to near- and onshore controls, we have only a limited quantitative understanding of how different local parameters influence the onshore response of tsunamis. Here, a numerical model based on the non-linear shallow water equations is first shown to agree well with analytical expressions developed for periodic long waves inundating over planar slopes. More than 13,000 simulations are then conducted to examine the effects variations in the wave characteristics, bed slopes, and bottom roughness have on maximum tsunami run-up and water velocity at the still water shoreline. While deviations from periodic waves and planar slopes affect the onshore dynamics, the details of these effects depend on a combination of factors. In general, the effects differ for breaking and non-breaking waves, and are related to the relative shift of the waves along the breaking–non-breaking wave continuum. Variations that shift waves toward increased breaking, such as steeper wave fronts, tend to increase the onshore impact of non-breaking waves, but decrease the impact of already breaking waves. The onshore impact of a tsunami composed of multiple waves can be different from that of a single wave tsunami, with the largest difference occurring on long, shallow onshore topographies. These results demonstrate that the onshore response of a tsunami is complex, and that using analytical expressions derived from simplified conditions may not always be appropriate.
Aqueous ferrofluids based on manganese and cobalt ferrites
Francisco Augusto Tourinho; Raymonde Franck; René Massart
1990-01-01
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
Brownian magnetic relaxation of water-based cobalt nanoparticle ferrofluids
Krishnan, Kannan M.
Brownian magnetic relaxation of water-based cobalt nanoparticle ferrofluids Y. Bao, A. B. Pakhomov of monodispersed 20 nm cobalt nanoparticles via a thermal decomposition method we have successfully transferred of water-based cobalt nanoparticle ferrofluids was measured at room temperature in the frequency range of 0
Wind waves as an element of a hydrodynamic coupled ocean-atmosphere model
NASA Astrophysics Data System (ADS)
Chalikov, D. V.; Bulgakov, K. Yu.
2015-05-01
A new approach to the coupled simulation of the ocean, atmosphere, and sea waves based on a detailed simulation of ocean-surface processes is described. The role of surface waves and the chain of energy and momentum transformation are briefly described: energy and momentum are transferred by wind to waves, turbulence, and surface currents through the field of surface pressure and tangential stress. Both energy and momentum accumulated in waves are transferred (with a lag) also to currents and turbulence within the ocean surface layer. The possibility of coupling atmosphere, ocean, and sea-wave models is considered.
NASA Astrophysics Data System (ADS)
Massel, S. R.; Done, T. J.
1993-11-01
Cyclone waves directly affect the density, structure and local distribution of coral assemblages by acting as agents of mortality and colony transport. Using the meteorological record, hydrodynamic formulations and risk analysis, we predict some demographic consequences of cyclones for massive corals growing in different regions of the Great Barrier Reef. Analysis of shear, compression and tension forces generated by waves indicate that corals firmly attached to solid substratum, even if only over a small proportion of their base, can resist all waves, regardless of colony size or shape, cyclone intensity or region. Waves are thus directly important as controls on colony-size frequency distributions only for weakly attached or unattached colonies. At 3 m depth, these colonies have a higher probability of escaping dislodgement in their first 10 years of life, the further north or south they are from 21°S, which is the latitude where severe cyclones are most frequent. At 21°S, corals at depths as great as 12m are exposed to the greatest likelihood of dislodgement. Possible implications of predicted increased storminess associated with global warming are briefly discussed.
Light scattering from a magnetically tunable dense random medium with dissipation: ferrofluid
NASA Astrophysics Data System (ADS)
Shalini, M.; Sharma, D.; Deshpande, A. A.; Mathur, D.; Ramachandran, Hema; Kumar, N.
2012-01-01
We present a semi-phenomenological treatment of light transmission through and its reflection from a ferrofluid which we regard as a magnetically tunable system of dense random dielectric scatterers with dissipation. Partial spatial ordering is introduced by the application of a transverse magnetic field that superimposes a periodic modulation on the dielectric randomness. This causes Bragg scattering that effectively enhances the scattering due to the disorder alone, and thus reduces the elastic mean free path towards Anderson localization. A theoretical treatment, based on invariant imbedding, gives a simultaneous decrease of the transmission and the reflection without change of incident linear polarisation as the spatial order is tuned magnetically to the Bragg condition, namely the light wave vector being equal to half the Bragg vector (Q). Our experimental observations are in qualitative agreement with these results. We have also given expressions for the transit (sojourn) time of the light, and for the light energy stored in the random medium under a steady illumination. The ferrofluid thus provides an interesting physical realization of effectively a "Lossy Anderson-Bragg" (LAB) cavity with which to study the effect of interplay of the spatial disorder, partial order and the dissipation on light transport. Given current interests in the light propagation, optical limiting and the storage of light in ferrofluids, the present work seems topical.
NASA Astrophysics Data System (ADS)
Moghimi, S.; Ozkan-Haller, H. T.; Thomson, J. M.; Zippel, S.
2014-12-01
The effect of the interaction between surface waves and tidal inlet circulation or river plumes on the full three dimensional (3D) circulation of the near-shore system is the main topic of this research. The process of wave breaking, either in deep or shallow waters, is followed by injection of turbulent kinetic energy into the underlying water column. This process modifies momentum eddy viscosity and tracer mixing properties. In this research we employed different two-equation one-dimensional vertical turbulence models to study breaking wave-induced turbulence for white-capping and depth-limited breaking cases. We used recent turbulence dissipation rate measurements using wave-following 'SWIFT' drifters at New River Inlet, North Carolina to verify the models. We improved our fully coupled 3D ocean-wave modelling system with new turbulence parameters and showed how the new turbulence characterizations could affect stratification and other plume properties in New River Inlet application.
Hoeke, R.; Storlazzi, C.; Ridd, P.
2011-01-01
This paper examines the relationship between offshore wave climate and nearshore waves and currents at Hanalei Bay, Hawaii, an exposed bay fringed with coral reefs. Analysis of both offshore in situ data and numerical hindcasts identify the predominance of two wave conditions: a mode associated with local trade winds and an episodic pattern associated with distant source long-period swells. Analysis of 10 months of in situ data within the bay show that current velocities are up to an order of magnitude greater during long-period swell episodes than during trade wind conditions; overall circulation patterns are also fundamentally different. The current velocities are highly correlated with incident wave heights during the swell episodes, while they are not during the modal trade wind conditions. A phase-averaged wave model was implemented with the dual purpose of evaluating application to bathymetrically complex fringing reefs and to examine the propagation of waves into the nearshore in an effort to better explain the large difference in observed circulation during the two offshore wave conditions. The prediction quality of this model was poorer for the episodic condition than for the lower-energy mode, however, it illustrated how longer-period swells are preferentially refracted into the bay and make available far more nearshore wave energy to drive currents compared to waves during modal conditions. The highly episodic circulation, the nature of which is dependent on complex refraction patterns of episodic, long-period swell has implications for flushing and sediment dynamics for incised fringing reef-lined bays that characterize many high islands at low latitudes around the world.
Hydrodynamical stellar models including rotation, internal gravity waves and atomic diffusion
Suzanne Talon; Corinne Charbonnel
In this paper, we develop a formalism in order to incorporate the contribution of internal gravity waves to the transport of angular momentum and chemicals over long time-scales in stars. We show that the development of a double peaked shear layer acts as a filter for waves, and how the asymmetry of this fi lter produces momentum extraction from the
Niederhaus, John; Ranjan, Devesh; Anderson, Mark; Oakley, Jason; Bonazza, Riccardo; Greenough, Jeff
2005-05-15
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.
Metachronal waves in the flagellar beating of Volvox and their hydrodynamic origin
Brumley, Douglas R.; Polin, Marco; Pedley, Timothy J.; Goldstein, Raymond E.
2015-06-03
-driven microrotors [18], and colloids in optical tweezers [19–21], as well as simu- lations of rotating helices [22], or spheres driven along fixed [23–27] or flexible [28,29] trajectories, have shown that under certain conditions hydrodynamic interactions alone can... polystyrene microspheres (Invitrogen, USA) at 2 #2; 1024 volume fraction, andmeasured using an open source particle image velocimetry (PIV) tool for Matlab (MatPIV) (figure 1). It was then decom- posed into radial and tangential components u(r, u, t) ¼ ur(r, u...
NASA Astrophysics Data System (ADS)
Dyer, Ashton; Blondin, J. M.; Reynolds, S. P.
2014-01-01
High resolution imaging of two young Type Ia supernova remnants (SNRs), Tycho and SN 1006, has revealed several morphological features which have resisted explanation with numerical simulations. One such feature is the presence of shocked ejecta blobs protruding beyond the mean forward shock radius. Two current theories explain the presence of such ejecta: highly dense ejecta shrapnel produced in the explosion penetrating the forward shock, or plumes generated by hydrodynamic instabilities long after the initial explosion. We investigate the shrapnel theory through hydrodynamic simulations in 2D and 3D of the evolution of dense ejecta clumps embedded in an exponential density profile, appropriate for Type Ia supernovae. We use high-resolution 2D simulations to identify relevant clump parameters which we investigate further in 3D. In contradiction to some former work, we find that sufficiently resolved clumps in 2D models shatter upon collision with the forward shock, yielding new protrusion features. In both 2D and 3D, shrapnel is capable of penetrating the forward shock, but the resultant protrusions in 3D simulations vary significantly from those in similar 2D runs, implying 2D simulations may not be an accurate method of investigating the shrapnel theory. We compare the our simulations with Chandra observations of projections seen in Tycho and SN 1006. This work was performed as part of NC State University's Undergraduate Research in Computational Astrophysics (URCA) program, an REU program supported by the National Science Foundation through award AST-1032736.
Geist, Eric L.; Jakob, Matthias; Wieczoreck, Gerald F.; Dartnell, Peter
2003-01-01
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.
Electromagnetic induction by ferrofluid in an oscillating heat pipe
NASA Astrophysics Data System (ADS)
Monroe, J. G.; Vasquez, E. S.; Aspin, Z. S.; Walters, K. B.; Berg, M. J.; Thompson, S. M.
2015-06-01
Thermal-to-electrical energy conversion was demonstrated using an oscillating heat pipe (OHP) filled with ferrofluid and equipped with an annular-type solenoid. The OHP was subjected to a 100 °C axial temperature difference allowing the ferrofluid to passively oscillate through the solenoid, thus accomplishing electromagnetic induction. The measured solenoid voltage consisted of aperiodic pulses with dominant frequencies between 2 and 5 Hz and peak-to-peak amplitudes approaching 1 mV. Despite exposure to the thermal and phase change cycling within the OHP, nanoparticle morphologies and magnetic properties of the ferrofluid remained intact. This energy harvesting method allows for combined thermal management and in-situ power generation.
Cytogenetic changes induced by aqueous ferrofluids in agricultural plants
NASA Astrophysics Data System (ADS)
R?cuciu, Mihaela; Creang?, Dorina
2007-04-01
In this paper, the authors present their results regarding the cellular division rate and the percentage of chromosomal aberrations in the root meristematic cells of agricultural plants when cultivated in the presence of different concentrations of aqueous ferrofluid, ranging between 10 and 250 ?L/L. The agricultural species ( Zea mays) with a major role in the life of people was chosen for the experimental project. The water-based ferrofluid was prepared following the chemical co-precipitation method, using tetramethylammonium hydroxide as magnetite core stabilizer. Microscopic investigations (cytogenetic tests) resulted in the evaluation of the mitotic and chromosomal aberration index. They appeared to increase following ferrofluid addition.
Drops deformation and magnetic permeability of a ferrofluid emulsion
Arthur Zakinyan; Yury Dikansky
2011-04-17
In the paper the novel soft magnetic composite system is investigated. A ferrofluid emulsion studied demonstrates the strong magnetic properties which are atypical for commonly known emulsions. Interaction of ferrofluid emulsions with a magnetic field is considered. Structural transformations in these media, such as deformation of emulsion microdroplets and emulsion inversion, are studied. The changes in the relative permeability of emulsion associated with structural transformations are investigated. The theory of the observed phenomena is developed, and the feasibility of effectively controlling the magnetic properties of ferrofluid emulsions by applying a magnetic field is demonstrated.
Ferrofluid dynamics: Spin-echo experiment
NASA Astrophysics Data System (ADS)
Lebedev, V. T.; Gordeev, G. P.; Panasiuk, E. A.; Kiss, L.; Cser, L.; Rosta, L.; Török, Gy.; Farago, B.
1993-04-01
Dependence of the dynamical behaviour of ferrofluid (FF) subsystems, i.e. nuclear and magnetic contributions to the scattering cross section, on the external magnetic field has been observed. In zero field, the nuclear subsystem of FF has a soft mode with the relation ?˜ q4, which can be explained by means of a dipole-bond fractal. This fractal gets broken by applying a magnetic field and then the motion of particles approaches ordinary diffusion, i.e ?˜ q2. The magnetic subsystem is superparamagnetic in a low field and it reveals the fast relaxation of spin components transversal to magnetization in a high field.
Polygonal micro-whirlpools induced in ferrofluids
Marcin Bacia; Weronika Lamperska; Jan Masajada; Slawomir Drobczynski; Maciej Marc
2015-04-23
We report on the observation of the polygonal whirlpools in the thin layer of ferrofluid under illumination with a laser beam carrying optical vortex and in the presence of a vertical magnetic field. This kind of structures have attracted attention after discovering a hexagonal storm in Saturns atmosphere. Our polygonal whirlpools were created in a closed system (no free surfaces) in micro scale (whirlpool diameter less than 20 micrometers) by the use of holographic optical tweezers. The polygonal shape was changed by varying the magnetic field strength or value of the optical vortex topological charge.
Polygonal micro-whirlpools induced in ferrofluids
Bacia, Marcin; Masajada, Jan; Drobczynski, Slawomir; Marc, Maciej
2015-01-01
We report on the observation of the polygonal whirlpools in the thin layer of ferrofluid under illumination with a laser beam carrying optical vortex and in the presence of a vertical magnetic field. This kind of structures have attracted attention after discovering a hexagonal storm in Saturns atmosphere. Our polygonal whirlpools were created in a closed system (no free surfaces) in micro scale (whirlpool diameter less than 20 micrometers) by the use of holographic optical tweezers. The polygonal shape was changed by varying the magnetic field strength or value of the optical vortex topological charge.
NASA Astrophysics Data System (ADS)
Suwa, T.; Imamura, F.; Sugawara, D.; Ogasawara, K.; Watanabe, M.; Hirahara, T.
2014-12-01
A tsunami simulator integrating a 3-D fluid simulation technology that runs on large-scale parallel computers using smoothed-particle hydrodynamics (SPH) method has been developed together with a 2-D tsunami propagation simulation technique using a nonlinear shallow water wave model. We use the 2-D simulation to calculate tsunami propagation of scale of about 1000km from epicenter to near shore. The 3-D SPH method can be used to calculate the water surface and hydraulic force that a tsunami can exert on a building, and to simulate flooding patterns at urban area of at most km scale. With our simulator we can also see three dimensional fluid feature such as complex changes a tsunami undergoes as it interacts with coastal topography or structures. As a result it is hoped that, e.g. , effect of the structures to dissipate waves energy passing over it can be elucidated. The authors utilize the simulator in the third of five fields of the Strategic Programs for Innovative Research, "Advanced Prediction Researches for Natural Disaster Prevention and Reduction," or the theme "Improvement of the tsunami forecasting system on the HPCI computer." The results of tsunami simulation using the K computer will be reported. We are going to apply it to a real problem of the disaster prevention in future.
Wake II model for hydrodynamic forces on marine pipelines for the wave plus current case
Ramirez Sabag, Said
1999-01-01
) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 24 9 Phase Parameter, tt, and P, , vs Local Keulegan-Carpenter. . . . . . 29 10 Phase Parameter, tI?and tt?, vs UJU for any Keulegan-Carpenter Number. . . 30 11 C, s vs Local Keulegan-Carpenter Number. 12 C? and C? vs Local Keulegan...-Carpenter Number. . . . . . . 30 . . . 31 13 Comparison Between the Lift Force Coefficients Ci (t) from PFMP, Wave Only and Wave Plus Current. . 14 Lift and Drag Coefficients vs Time 15 Comparison of Predicted and Measured Effective Velocity at Nitc=10, U...
Richard I. Klein; Christopher F. McKee; Philip Colella
1994-01-01
The interstellar medium (ISM) is inhomogeneous, with clouds of various temperatures and densities embedded in a tenuous intercloud medium. Shocks propagating through the ISM can ablate or destroy the clouds, at the same time significantly altering the properties of the intercloud medium. This paper presents a comprehensive numerical study of the simplest case of the interaction between a shock wave
Hydrodynamics of a cold one-dimensional fluid: the problem of strong shock waves
Pablo I. Hurtado
2005-01-01
We study a shock wave induced by an infinitely massive piston propagating into a one-dimensional cold gas. The cold gas is modelled as a collection of hard rods which are initially at rest, so the temperature is zero. Most of our results are based on simulations of a gas of rods with binary mass distribution, and we partcularly focus on
Ferrofluids, complex particle dynamics and braid description
NASA Astrophysics Data System (ADS)
Skjeltorp, Arne T.; Clausen, Sigmund; Helgesen, Geir
2001-05-01
Finely divided magnetic matter is important in many areas of science and technology. A special sub-class of systems are made up of freely moving particles suspended in a carrier liquid where the magnetic interactions play an important role in the actual structure formation and dynamical behaviour. These include ferrofluids, which are colloids of magnetic particles dispersed in carrier fluids, magnetic micro-beads, which are micrometer sized plastic beads loaded with iron oxide, and nonmagnetic particles dispersed in ferrofluids, forming the so-called "magnetic holes". How, in a simple and forceful way, is it possible to characterise the dynamics of systems with several moving components like dispersed magnetic particles subjected to external magnetic fields? The methods based on the theory of braids may provide the answer. Braid theory is a sub-field of mathematics known as topology. It involves classifying different ways of tracing curves in space. The topological description of braids thus provides a simple and concise language for describing the dynamics of a system of moving particles as if they perform a complicated dance as they move about one another, and the braid encodes the choreography of this dance.
NASA Astrophysics Data System (ADS)
Schwaiger, H. F.
2008-12-01
The impact of a deformable object with a body of water, such as with tsunamigenic, subaerial landslides, can lead to a complex near-field wave structure that can involve the generation of a substantial air cavity. The structure of the initiation and collapse of this cavity depends on the impact angle, velocity and geometry of the impacting landslide and is a likely source of the significant variations in the efficiency of energy transfer from landslide motion to the resulting wave energy. The severe deformation of the interfaces between landslide material, water and air can be problematic to simulate with many numerical methods. Eulerian grid- based methods are disadvantaged by their inherent difficulty tracking interfaces between phases. While Lagrangian grid-based methods naturally track material interfaces, they generally have difficulties with the significant deformation during the impact. Combination grid-based methods, such as the Arbitrary Lagrangian-Eulerian method, have been constructed to both allow for large deformation and track Lagrangian motion, and have been applied to modeling tsunamigenic landslides. In contrast to these grid- based methods, Lagrangian particle methods, such as Smoothed Particle Hydrodynamics (SPH), do not rely on an underlying mesh and both allow for large deformations and the tracking of Lagrangian motion. We have implemented an SPH model to study this impact process, cavity generation, and energy transfer. We treat the landslide as an incompressible, viscous fluid and the water as an incompressible, inviscid fluid. We present numerical experiments showing the dependence of the predicted solitary wave motion on the velocity and impact angle of the landslide, as well as the geometry of the impacting front of the landslide.
Ferrofluid surface and volume flows in uniform rotating magnetic fields
Elborai, Shihab M. (Shihab Mahmoud), 1977-
2006-01-01
Ferrofluid surface and volume effects in uniform dc and rotating magnetic fields are studied. Theory and corroborating measurements are presented for meniscus shapes and resulting surface driven flows, spin-up flows, and ...
Ferrohydrodynamic evaluation of rotational viscosity and relaxation in certain ferrofluids
NASA Astrophysics Data System (ADS)
Patel, Rajesh
2012-07-01
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.
Lattice Kinetic Formulation for Ferrofluids Paul J. Dellar
Dellar, Paul J.
, multiple relaxation time collision operators, magnetoviscosity, complex fluids, polar fluids To appear such as high performance seals and bearings. Ferrofluids also raise interesting questions in basic fluid behavior such as
NASA Astrophysics Data System (ADS)
Suslov, Sergey A.; Bozhko, Alexandra A.; Putin, Gennady F.; Sidorov, Alexander S.
2012-11-01
Study of Boussinesq convection in a vertical differentially heated fluid layer is one of classical problems in hydrodynamics. It is well known that as the value of fluid's Grashof number increases the basic flow velocity profile becomes unstable with respect to stationary shear-driven disturbances (at Prandtl numbers Pr < 12.5) or thermogravitational waves propagating vertically (at larger values of Prandtl number). However linear stability studies of a similar flow of magnetopolarizable nanosuspensions (ferrofluids) placed in a uniform magnetic field perpendicular to a fluid layer predicted the existence of a new type of instability, oblique waves, that arise due to the differential local magnetisation of a non-uniformly heated fluid. The existence of such (thermomagnetic) waves has now been confirmed experimentally using a kerosene-based ferrofluid with magnetite particles of the average size of 10 nm stabilized with oleic acid. The heat transfer rate measurements using thermocouples and flow visualization using a thermosensitive film and an infrared camera have been performed. Perturbation energy analysis has been used to determine the physical nature of various observed instability patterns and quantitatively distinguish between thermogravitational and thermomagnetic waves.
Thin viscous ferrofluid film in a magnetic field
NASA Astrophysics Data System (ADS)
Conroy, Devin T.; Matar, Omar K.
2015-09-01
We consider a thin, ferrofluidic film flowing down an inclined substrate, under the action of a magnetic field, bounded above by an inviscid gas. Its dynamics are governed by a coupled system of the steady Maxwell's, the Navier-Stokes, and the continuity equations. The magnetization of the film is a function of the magnetic field and may be prescribed by a Langevin function. We make use of a long-wave reduction in order to solve for the dynamics of the pressure and velocity fields inside the film. In addition, we investigate the problem in the limit of a large magnetic permeability. Imposition of appropriate interfacial conditions allows for the construction of an evolution equation for the interfacial shape via use of the kinematic condition. The resultant one-dimensional equations are solved numerically using spectral methods. The magnetic effects give rise to a non-local contribution. We conduct a parametric study of both the linear and nonlinear stabilities of the system in order to evaluate the effects of the magnetic field. Through a linear stability analysis, we verify that the Maxwell's pressure generated from a normally applied magnetic field is destabilizing and can be used to control the size and shape of lobes and collars on the free surface. We also find that in the case of a falling drop, the magnetic field causes an increase in the velocity and capillary ridge of the drop.
Characterizing ferrofluid spin-up flow in rotating uniform magnetic fields
Dozier, Kahlil A
2014-01-01
A ferrofluid is a collection of nanoscale ferromagnetic particles with a stabilizing surfactant in a liquid to form a colloid. The dynamic behavior of ferrofluids in the presence of magnetic fields has long been an area ...
Ferrofluid spin-up flows from uniform and non-uniform rotating magnetic fields
Khushrushahi, Shahriar Rohinton
2010-01-01
When ferrofluid in a cylindrical container is subjected to a rotating azimuthally directed magnetic field, the fluid "spins up" into an almost rigid-body rotation where ferrofluid nanoparticles have both a linear and an ...
Andreev, Pavel A
2015-03-01
The quantum hydrodynamic (QHD) model of charged spin-1/2 particles contains physical quantities defined for all particles of a species including particles with spin-up and with spin-down. Different populations of states with different spin directions are included in the spin density (the magnetization). In this paper I derive a QHD model, which separately describes spin-up electrons and spin-down electrons. Hence electrons with different projections of spins on the preferable direction are considered as two different species of particles. It is shown that the numbers of particles with different spin directions do not conserve. Hence the continuity equations contain sources of particles. These sources are caused by the interactions of the spins with the magnetic field. Terms of similar nature arise in the Euler equation. The z projection of the spin density is no longer an independent variable. It is proportional to the difference between the concentrations of the electrons with spin-up and the electrons with spin-down. The propagation of waves in the magnetized plasmas of degenerate electrons is considered. Two regimes for the ion dynamics, the motionless ions and the motion of the degenerate ions as the single species with no account of the spin dynamics, are considered. It is shown that this form of the QHD equations gives all solutions obtained from the traditional form of QHD equations with no distinction of spin-up and spin-down states. But it also reveals a soundlike solution called the spin-electron acoustic wave. Coincidence of most solutions is expected since this derivation was started with the same basic equation: the Pauli equation. Solutions arise due to the different Fermi pressures for the spin-up electrons and the spin-down electrons in the magnetic field. The results are applied to degenerate electron gas of paramagnetic and ferromagnetic metals in the external magnetic field. The dispersion of the spin-electron acoustic waves in the partially spin-polarized degenerate neutron matter are also considered. PMID:25871228
NASA Astrophysics Data System (ADS)
Andreev, Pavel A.
2015-03-01
The quantum hydrodynamic (QHD) model of charged spin-1/2 particles contains physical quantities defined for all particles of a species including particles with spin-up and with spin-down. Different populations of states with different spin directions are included in the spin density (the magnetization). In this paper I derive a QHD model, which separately describes spin-up electrons and spin-down electrons. Hence electrons with different projections of spins on the preferable direction are considered as two different species of particles. It is shown that the numbers of particles with different spin directions do not conserve. Hence the continuity equations contain sources of particles. These sources are caused by the interactions of the spins with the magnetic field. Terms of similar nature arise in the Euler equation. The z projection of the spin density is no longer an independent variable. It is proportional to the difference between the concentrations of the electrons with spin-up and the electrons with spin-down. The propagation of waves in the magnetized plasmas of degenerate electrons is considered. Two regimes for the ion dynamics, the motionless ions and the motion of the degenerate ions as the single species with no account of the spin dynamics, are considered. It is shown that this form of the QHD equations gives all solutions obtained from the traditional form of QHD equations with no distinction of spin-up and spin-down states. But it also reveals a soundlike solution called the spin-electron acoustic wave. Coincidence of most solutions is expected since this derivation was started with the same basic equation: the Pauli equation. Solutions arise due to the different Fermi pressures for the spin-up electrons and the spin-down electrons in the magnetic field. The results are applied to degenerate electron gas of paramagnetic and ferromagnetic metals in the external magnetic field. The dispersion of the spin-electron acoustic waves in the partially spin-polarized degenerate neutron matter are also considered.
Magneto-optical and rheological behaviors of oil-based ferrofluids and magnetorheological fluids
NASA Astrophysics Data System (ADS)
Getzie, Travis
The magneto-optical and rheological behaviors of magnetic fluids and magnetorheological (MR) fluids have been investigated. A magneto-optical apparatus was constructed which enabled us to investigate the birefringence and dichroism of ferrofluids at various levels of applied magnetic field. Specifically, the effects of the film thickness of oil-based ferrofluids and the concentration of surfactant in the oil-based ferrofluids on their magneto-optical behavior were investigated. A commercial magneto-rheological instrument (Physica MCR 301, Anton Paar) equipped with a cone-and-plate fixture was employed to investigate the transient and steady-state shear flow of both ferrofluids and MR fluids as a function of shear rate at various levels of applied magnetic fields. The rheological investigation has enabled us to determine the effect of applied magnetic field on the shear viscosity and yield stress of ferrofluids and MR fluids. A special ferrofluid was prepared by filtering out nearly all of the surfactant and small particles in an oil-based ferrofluid. We then compared its magneto-optical and rheological behaviors with those of an unfiltered ferrofluid. Further, we have found that the ferrofluid with a lower concentration of surfactant gave rise to larger birefringence and yield stress, and stronger shear thinning behavior than the ferrofluid containing a higher concentration of surfactant. This observation has lead us to conclude that an increase in unbound surfactant in a ferrofluid hindered chain formation of magnetic particles, leading to a decrease in the optical and rheological behaviors of the ferrofluid. Optical microscopy confirmed no visible chain formation of magnetic particles in the ferrofluid having a high concentration of surfactant owing to weak yield stress, birefringence, and shear thinning. On the other hand, we observed from optical microscopy that the filtered ferrofluid gave rise to larger yield stress, birefringence, and stronger shear thinning behavior. Thus, using optical microscopy we were able to explain the magneto-optical and rheological behaviors of the ferrofluids and magnetorheological fluids investigated.
Sink-float ferrofluid separator applicable to full scale nonferrous scrap separation
NASA Technical Reports Server (NTRS)
1973-01-01
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.
Pampori, Adam; Keledjian, Kaspar; Tosun, Cigdem; Schwartzbauer, Gary; Ivanova, Svetlana; Gerzanich, Volodymyr
2014-01-01
Abstract Traumatic brain injury (TBI) caused by an explosive blast (blast-TBI) is postulated to result, in part, from transvascular transmission to the brain of a hydrodynamic pulse (a.k.a., volumetric blood surge, ballistic pressure wave, hydrostatic shock, or hydraulic shock) induced in major intrathoracic blood vessels. This mechanism of blast-TBI has not been demonstrated directly. We tested the hypothesis that a blast wave impacting the thorax would induce a hydrodynamic pulse that would cause pathological changes in the brain. We constructed a Thorax-Only Blast Injury Apparatus (TOBIA) and a Jugular-Only Blast Injury Apparatus (JOBIA). TOBIA delivered a collimated blast wave to the right lateral thorax of a rat, precluding direct impact on the cranium. JOBIA delivered a blast wave to the fluid-filled port of an extracorporeal intravenous infusion device whose catheter was inserted retrograde into the jugular vein, precluding lung injury. Long Evans rats were subjected to sublethal injury by TOBIA or JOBIA. Blast injury induced by TOBIA was characterized by apnea and diffuse bilateral hemorrhagic injury to the lungs associated with a transient reduction in pulse oximetry signals. Immunolabeling 24?h after injury by TOBIA showed up-regulation of tumor necrosis factor alpha, ED-1, sulfonylurea receptor 1 (Sur1), and glial fibrillary acidic protein in veins or perivenular tissues and microvessels throughout the brain. The perivenular inflammatory effects induced by TOBIA were prevented by ligating the jugular vein and were reproduced using JOBIA. We conclude that blast injury to the thorax leads to perivenular inflammation, Sur1 up-regulation, and reactive astrocytosis resulting from the induction of a hydrodynamic pulse in the vasculature. PMID:24673157
Simard, J Marc; Pampori, Adam; Keledjian, Kaspar; Tosun, Cigdem; Schwartzbauer, Gary; Ivanova, Svetlana; Gerzanich, Volodymyr
2014-07-15
Traumatic brain injury (TBI) caused by an explosive blast (blast-TBI) is postulated to result, in part, from transvascular transmission to the brain of a hydrodynamic pulse (a.k.a., volumetric blood surge, ballistic pressure wave, hydrostatic shock, or hydraulic shock) induced in major intrathoracic blood vessels. This mechanism of blast-TBI has not been demonstrated directly. We tested the hypothesis that a blast wave impacting the thorax would induce a hydrodynamic pulse that would cause pathological changes in the brain. We constructed a Thorax-Only Blast Injury Apparatus (TOBIA) and a Jugular-Only Blast Injury Apparatus (JOBIA). TOBIA delivered a collimated blast wave to the right lateral thorax of a rat, precluding direct impact on the cranium. JOBIA delivered a blast wave to the fluid-filled port of an extracorporeal intravenous infusion device whose catheter was inserted retrograde into the jugular vein, precluding lung injury. Long Evans rats were subjected to sublethal injury by TOBIA or JOBIA. Blast injury induced by TOBIA was characterized by apnea and diffuse bilateral hemorrhagic injury to the lungs associated with a transient reduction in pulse oximetry signals. Immunolabeling 24 h after injury by TOBIA showed up-regulation of tumor necrosis factor alpha, ED-1, sulfonylurea receptor 1 (Sur1), and glial fibrillary acidic protein in veins or perivenular tissues and microvessels throughout the brain. The perivenular inflammatory effects induced by TOBIA were prevented by ligating the jugular vein and were reproduced using JOBIA. We conclude that blast injury to the thorax leads to perivenular inflammation, Sur1 up-regulation, and reactive astrocytosis resulting from the induction of a hydrodynamic pulse in the vasculature. PMID:24673157
Magneto-viscosity of MnZn-ferrite ferrofluid
NASA Astrophysics Data System (ADS)
Thirupathi, Gadipelly; Singh, Rajender
2014-09-01
Mn0.75Zn0.25Fe2O4 (MZF) ferrofluid was synthesized using a precipitation method in ethylene glycol colloidal media. The x-ray diffraction and transmission electron microscope studies show nanophase of the MZF ultra fine nanoparticles. The magnetization (M) vs magnetic field (H) show zero coercivity and high saturation field characteristic of superparamagnetic behavior. The dynamic light scattering (DLS) data show the formation of aggregates or clusters with size distribution ranging from 50 to 600 nm. Magneto-viscosity of the ferrofluid is studied using rheological measurements under magnetic field up to 1.3 T. The behavior of shear rate vs effective shear viscosity (?) plot in zero and higher magnetic field changes from non-Newtonian to Newtonian as shear rate increases. At a steady shear rate irreversible nonlinear behavior is observed in ? vs H plots. The data indicate the particle size distribution and formation of chains in the ferrofluid with increase in magnetic field.
Experimental demonstration of metamaterial "multiverse" in a ferrofluid.
Smolyaninov, Igor I; Yost, Bradley; Bates, Evan; Smolyaninova, Vera N
2013-06-17
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
Experimental demonstration of metamaterial ``multiverse'' in a ferrofluid
NASA Astrophysics Data System (ADS)
Smolyaninov, Igor I.; Yost, Bradley; Bates, Evan; Smolyaninova, Vera N.
2013-06-01
Extraordinary light rays propagating inside a hyperbolic metamaterial look similar to particle world lines in a 2+1 dimensional Minkowski spacetime [1]. 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.
Ferrofluid nucleus phase transitions in an external uniform magnetic field
B. M. Tanygin; S. I. Shulyma; V. F. Kovalenko; M. V. Petrychuk
2015-02-18
Phase transition between massive dense phase and diluted superparamagnetic phase is studied by means of direct molecular dynamics simulation. Equilibrium structures of ferrofluid aggregate nucleus are obtained for different values of temperature and external magnetic field magnitude. For the ferrofluid phase diagram (coordinates "field-temperature"): approximate match of experiment and simulation is shown. Obtained phase coexistence curve has opposite trend compare to some of known theoretical results. This contradiction is related to postulating and comparing of the free energy of only simplest ferrofluid structures: diluted superparamagnetic phase, linear chains of the particles, and dense globes. The present results provide more fine structure of transition from "linear chains" to "dense globes" phase, e.g. through the ring assembly structure.
Magnetically tunable terahertz magnetoplasmons in ferrofluid-filled photonic crystals
NASA Astrophysics Data System (ADS)
Fan, Fei; Chen, Sai; Lin, Wei; Miao, Yin-Ping; Chang, Sheng-Jiang; Liu, Bo; Wang, Xiang-Hui; Lin, Lie
2013-10-01
We investigated terahertz (THz) magneto-optical properties of a ferrofluid and a ferrofluid-filled photonic crystal (FFPC) by using the THz time-domain spectroscopy. A magnetoplasmon resonance splitting and an induced THz transparency phenomenon were demonstrated in the FFPC. The further investigation reveals that the induced transparency originates from the interference between magnetoplasmon modes in the hybrid magneto-optical system of FFPC, and the THz modulation with a 40% intensity modulation depth can be realized in this induced transparency frequency band. This device structure and its tunabilty scheme will have great potential applications in THz filtering, modulation and sensing.
Dynamics of concentrated ferrofluid with labelled particles
NASA Astrophysics Data System (ADS)
Lebedev, V. T.; Torok, Gy.; Kali, Gy.; Cser, L.; Brulet, A.; Orlova, D. N.; Sibilev, A. I.
1999-07-01
In the study of ferrofluid dynamics the separation of self and pair correlation is the essential problem at both intermediate and high concentrations of the magnetic phase. The neutron spin-echo (NSE) total scattering function S t(q, t)=?S p(q, t)+(1-?)S s(q, t) contains both contributions, where the parameter ?= ?p/( ?p+ ?s) depends on the corresponding cross sections ?s,p. To distinguish these different kinds of dynamics we eliminated one of them by using a mixture of magnetic particles with different scattering amplitudes and concentrations. The NSE experiments (LLB, CE-Saclay) at momentum transfer q1?0.4 nm ˜1/ Dp ( Dp is the particle diameter) and q 2?0.7 nm>1/D p have been carried out for these opposite situations. The functions S p(q, t), S s(q, t) , from these data behave quite differenly. The autocorrelations reveal a stretched relaxation at low q: S s(q, t)= exp[-q 2?(t)/2] , where ?( t)=2 Dt? is the squared particle displacement, the exponent ?=0.5±0.1 at q1, and ?=0.8±0.1 at q2. The magnitude ?<1 indicates the strong influence of dipole forces on the motion of a particle. It resembles the segmental relaxation in a polymer chain. On the other hand, the pair correlations show the oscillations (period˜40 ns, amplitude˜1 nm) mixed with diffusion.
Magnetic sensing with ferrofluid and fiber optic connectors.
Homa, Daniel; Pickrell, Gary
2014-01-01
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
A study of curie-weiss behaviour in ferrofluids
NASA Astrophysics Data System (ADS)
Holmes, M.; O'Grady, K.; Popplewell, J.
1990-04-01
In this paper we have investigated concentration effects on the temperature variation of ac susceptibility for a Fe 3O 4 ferrofluid. Our measurements show deviation from classical Langevin theory and a non-linear Curie-Weiss behaviour. This is attributed to the effects of interparticle interactions.
Microwave absorption in ferrofluid composites containing metallic particles
NASA Astrophysics Data System (ADS)
Popplewell, J.; Davies, P.; Llewellyn, J. P.
1987-03-01
The magnetic dichroism of composites consisting of metallic particles (Ag, Sn, C, Cu or Al) in a ferrofluid has been measured at a wavelength of 3 mm as a function of particle concentration and applied magnetic field. Absorptions as large as 60% are observed in fields of less than 60 Oe in thin film samples 1 mm thick.
Improving the efficiency of electric machines using ferrofluids
A. Nethe; Th Scholz; H.-D. Stahlmann
2006-01-01
Ferrofluids have a growing importance in technical and medical applications since stable suspensions of magnetic nanoparticles in carrier fluids can be produced. The application of these strong paramagnetic fluids in electric machines by filling the air-gap between stator and rotor to increase the force in linear and the momentum in rotating machines offers an interesting possibility to improve efficiency and
Rheological characterization of a magnetorheological ferrofluid using iron nitride nanoparticles
NASA Astrophysics Data System (ADS)
Armijo, Leisha M.; Ahuré-Powell, Louise A.; Wereley, Norman M.
2015-05-01
Magnetorheology of a magnetorheological ferrofluid (MRFF) was investigated to study the role of a ferromagnetic nanoparticle (NP) additive in magnetorheological fluids (MRFs). Iron nitride (Fe16N2) NPs, nominally within the diameter range of ˜16-45 nm (spherical NPs) and ˜30-66 nm (cubic NPs), were coated with carboxy-polyethylene glycol (carboxy-PEG) and dispersed in silicone oil in order to produce a magnetic carrier fluid or ferrofluid for two solids loadings: 2 vol. % and 5 vol. %. Conventional spherical carbonyl iron (CI) particles, varying in diameter from 6 to 10 ?m, were suspended in the ferrofluid at 25 vol. % solids loading. Rheological properties of the MRFF synthesized with the carboxy-PEG-based ferromagnetic carrier fluid were compared to the MRF synthesized with silicone oil to determine how ferrofluid can influence dynamic viscosity and yield stress. Rheological measurements of both MRF and MRFF samples were carried out using a Paar Physica 300 rheometer to estimate the field-off viscosity and to measure flow curves (i.e., shear stress vs. shear rate) as a function of magnetic field. A Bingham-plastic model was used to characterize the flow curves, and results show that there is an increase in the dynamic viscosity of the MRFF over the MRF. The ferromagnetic carrier fluid greatly increases yield stress as only 2 vol. % of added carboxy-PEG NPs improves the yield stress performance by almost 5%. A second MRFF sample synthesized with 5 vol. % of added carboxy-PEG NPs contained in the ferrofluid significantly enhanced the yield stress performance by 13% over the MRF at the same CI solids loading (25 vol. %).
Dynamics of Single Chains of Suspended Ferrofluid Particles
NASA Technical Reports Server (NTRS)
Cutillas, S.; Liu, J.
1999-01-01
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
Gu, Yu; Valentino, Gianna; Mongeau, Eric
2014-02-01
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
Smolyaninov, Igor I; Smolyaninova, Vera N; Smolyaninov, Alexei I
2015-08-28
In the presence of an external magnetic field, cobalt nanoparticle-based ferrofluid forms a self-assembled hyperbolic metamaterial. The wave equation, which describes propagation of extraordinary light inside the ferrofluid, exhibits 2+1 dimensional Lorentz symmetry. The role of time in the corresponding effective three-dimensional Minkowski space-time is played by the spatial coordinate directed along the periodic nanoparticle chains aligned by the magnetic field. Here, we present a microscopic study of point, linear, planar and volume defects of the nanoparticle chain structure and demonstrate that they may exhibit strong similarities with such Minkowski space-time defects as magnetic monopoles, cosmic strings and the recently proposed space-time cloaks. Experimental observations of such defects are described. PMID:26217055
NASA Astrophysics Data System (ADS)
Benson, Philip M.; Meredith, Philip G.; Platzman, Ellen S.
2003-10-01
Pore fabric anisotropy is a common feature of many sedimentary rocks. In this paper we report results from a comparative study on the anisotropy of a porous sandstone (Crab Orchard) using anisotropy of magnetic susceptibility (AMS), acoustic wave velocity and fluid permeability techniques. Initially, we characterise the anisotropic pore fabric geometry by impregnating the sandstone with magnetic ferro-fluid and measuring its AMS. The results are used to guide subsequent measurements of the anisotropy of acoustic wave velocity and fluid permeability. These three independent measures of anisotropy are then directly compared. Results show strong positive correlation between the principal directions given from the AMS, velocity anisotropy and permeability anisotropy. Permeability parallel to the macroscopic crossbedding observed in the sandstone is 240% higher than that normal to it. P and S-wave velocity anisotropy and AMS show mean values of 19.1%, 4.8% and 3.8% respectively, reflecting the disparate physical properties measured.
Fumitaka Nakamura; Christopher F. McKee; Richard I. Klein; Robert T. Fisher
2005-11-01
The effect of smooth cloud boundaries on the interaction of steady planar shock waves with interstellar clouds is studied using a high-resolution local AMR technique with a second-order accurate axisymmetric Godunov hydrodynamic scheme. A 3D calculation is also done to confirm the results of the 2D ones. We consider an initially spherical cloud whose density distribution is flat near the cloud center and has a power-law profile in the cloud envelope. When an incident shock is transmitted into a smooth cloud, velocity gradients in the cloud envelope steepen the smooth density profile at the upstream side, resulting in a sharp density jump having an arc-like shape. Such a ``slip surface'' forms immediately when a shock strikes a cloud with a sharp boundary. For smoother boundaries, the formation of slip surface and therefore the onset of hydrodynamic instabilities are delayed. Since the slip surface is subject to the Kelvin-Helmholtz and Rayleigh-Taylor instabilities, the shocked cloud is eventually destroyed in $\\sim 3-10$ cloud crushing times. After complete cloud destruction, small blobs formed by fragmentation due to hydrodynamic instabilities have significant velocity dispersions of the order of 0.1 $v_b$, where $v_b$ is the shock velocity in the ambient medium. This suggests that turbulent motions generated by shock-cloud interaction are directly associated with cloud destruction. The interaction of a shock with a cold HI cloud should lead to the production of a spray of small HI shreds, which could be related to the small cold clouds recently observed by Stanimirovic & Heiles (2005). The linewidth-size relation obtained from our 3D simulation is found to be time-dependent. A possibility for gravitational instability triggered by shock compression is also discussed.
Preparation of a biocompatible magnetic film from an aqueous ferrofluid
NASA Astrophysics Data System (ADS)
Albornoz, Cecilia; Jacobo, Silvia E.
2006-10-01
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.
Tritium test of a ferro-fluidic rotary seal
Antipenkov, A.; Day, C.; Adami, H. D. [Forschungszentrum Karlsruhe, Inst. for Technical Physics, Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen, 76344 (Germany)
2008-07-15
The ferro-fluidic seal is being investigated as an internal rotary seal for tritium compatible mechanical roots type vacuum pumps. After its successful testing with helium and integration into a small (250 m{sup 3}/h) test roots pump, the seal, made as a cartridge, has been integrated into a special test unit and is currently being tested with tritium in order to define the leak rates and the possible degradation of the ferro-fluid under long term exposure to tritium radiation. The tritium pressure from one side of the seal is 0.125 MPa, the nitrogen pressure from the other side is 0.075 MPa, the rotation speed is maintained at 1500 rpm. The tritium leak through the cartridge contributes to the tritium concentration in the nitrogen, which is continuously measured by an ionisation chamber; the pressure in both chambers is continuously registered by precise pressure gauges. The experimental program is discussed. (authors)
Energy conversion in ferrofluids: Magnetic nanoparticles as motors or generators
F. Gazeau; C. Baravian; J.-C. Bacri; R. Perzynski; M. I. Shliomis
1997-01-01
We submit a CoFe2O4 ferrofluid in rigid rotation (and then in a Couette flow) to an alternating magnetic field. Rotational viscosity and transverse magnetization are measured simultaneously. Depending on the relative values of fluid vorticity and field frequency, the magnetic particles behave as nanomotors or nanogenerators. It demonstrates the energy conversion between the magnetic and kinetic degrees of freedom of
Moridis, George J. (Oakland, CA); Oldenburg, Curtis M. (Mill Valley, CA)
2001-01-01
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.
Coupling of blocking and melting in cobalt ferrofluids Tianlong Wen,1,a
Krishnan, Kannan M.
Coupling of blocking and melting in cobalt ferrofluids Tianlong Wen,1,a Wenkel Liang,2 and Kannan M performed on ferrofluids of cobalt magnetic nanoparticles MNPs in various organic solvent. Two peaks, one Brownian relaxation of cobalt MNPs when TB TM by in- specting the M spectrum8 of the FFs. Cobalt MNPs were
Effects of surfactant friction on Brownian magnetic relaxation in nanoparticle ferrofluids
Krishnan, Kannan M.
nanoparticles in a ferrofluid due to binding of organic molecules is a possible tool for detection of biomolecules in solution. We investigate frequency- and temperature-dependent magnetic behavior of model ferro-fluids of surfactant-coated Co nanoparticles, 20 nm in diameter, in dichlorobenzene in a wide concentration range
NASA Astrophysics Data System (ADS)
Yasuda, Seiji; Miura, Hitoshi; Nakamoto, Taishi
2009-11-01
We carried out three-dimensional hydrodynamics simulations of the disruption of a partially-molten dust particle exposed to high-speed gas flow to examine the compound chondrule formation due to mutual collisions between the fragments (fragment-collision model; [Miura, H., Yasuda, S., Nakamoto, T., 2008a. Icarus194, 811-821]). In the shock-wave heating model, which is one of the most plausible models for chondrule formation, the gas friction heats and melts the surface of the cm-sized dust particle (parent particle) and then the strong gas ram pressure causes the disruption of the molten surface layer. The hydrodynamics simulation shows details of the disruptive motion of the molten surface, production of many fragments and their trajectories parting from the parent particle, and mutual collisions among them. In our simulation, we identified 32 isolated fragments extracted from the parent particle. The size distribution of the fragments was similar to that obtained from the aerodynamic experiment in which a liquid layer was attached to a solid core and it was exposed to a gas flow. We detected 12 collisions between the fragments, which may result in the compound chondrule formation. We also analyzed the paths of all the fragments in detail and found the importance of the shadow effect in which a fragment extracted later blocks the gas flow toward a fragment extracted earlier. We examined the collision velocity and impact parameter of each collision and found that 11 collisions should result in coalescence. It means that the ratio of coalescent bodies to single bodies formed in this disruption of a parent particle is R=11/(32-11)=0.52. We concluded that compound chondrule formation can occur just after the disruption of a cm-sized molten dust particle in shock-wave heating.
NASA Astrophysics Data System (ADS)
Rajnak, Michal; Petrenko, Viktor I.; Avdeev, Mikhail V.; Ivankov, Olexandr I.; Feoktystov, Artem; Dolnik, Bystrik; Kurimsky, Juraj; Kopcansky, Peter; Timko, Milan
2015-08-01
Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fields. Here, we report on formation of visually observable patterns in a diluted low-polarity ferrofluid exposed to external electric fields. This presents a specific type of ferrofluid structure driven by a combined effect of electrohydrodynamics and electrical body forces. The free charge and permittivity variation are considered to play a key role in the observed phenomenon. The corresponding changes in the ferrofluid structure have been found at nanoscale as well. By small-angle neutron scattering (SANS), we show that the magnetic nanoparticles aggregate in direct current (dc) electric field with a strong dependence on the field intensity. The anisotropic aggregates preferably orient in the direction of the applied electric field. Conducting SANS experiments with alternating current (ac) electric fields of various frequencies, we found a critical frequency triggering the aggregation process. Our experimental study could open future applications of ferrofluids based on insulating liquids.
Synchronization via Hydrodynamic Interactions
NASA Astrophysics Data System (ADS)
Kendelbacher, Franziska; Stark, Holger
2013-12-01
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.
A S Monin
1986-01-01
The current state of the classical theory of hydrodynamic instability is examined by viewing the mathematical theory (as well as experimental data) concerning the randomization of motions of liquids and gases as a problem in bifurcation theory of families of dynamic systems. Along with a discussion of the theory of linear operators encountered in hydrodynamics (a theory which is still
Hydrodynamics of insect spermatozoa
NASA Astrophysics Data System (ADS)
Pak, On Shun; Lauga, Eric
2010-11-01
Microorganism motility plays important roles in many biological processes including reproduction. Many microorganisms propel themselves by propagating traveling waves along their flagella. Depending on the species, propagation of planar waves (e.g. Ceratium) and helical waves (e.g. Trichomonas) were observed in eukaryotic flagellar motion, and hydrodynamic models for both were proposed in the past. However, the motility of insect spermatozoa remains largely unexplored. An interesting morphological feature of such cells, first observed in Tenebrio molitor and Bacillus rossius, is the double helical deformation pattern along the flagella, which is characterized by the presence of two superimposed helical flagellar waves (one with a large amplitude and low frequency, and the other with a small amplitude and high frequency). Here we present the first hydrodynamic investigation of the locomotion of insect spermatozoa. The swimming kinematics, trajectories and hydrodynamic efficiency of the swimmer are computed based on the prescribed double helical deformation pattern. We then compare our theoretical predictions with experimental measurements, and explore the dependence of the swimming performance on the geometric and dynamical parameters.
Hydrodynamic forces due to waves and a current induced on a pipeline placed in an open trench
Lee, Jaeyoung
1991-01-01
. The movements of the pipe were converted to horizontal and vertical forces. The drag, inertia and lift force coefficients were obtained in each group of Reynolds numbers by using the Morison equation and the least square method. The maximum measured forces... are also presented in the dimensionless forms. The results showed 30 ? 60% reductions in drag and lift coefficients for the trenched pipe in wave ? current flow, compared to those recommended by det Norske Veritas for the smooth surface pipe on the flat...
The effect of suspended Fe3O4 nanoparticle size on magneto-optical properties of ferrofluids
NASA Astrophysics Data System (ADS)
Brojabasi, Surajit; Muthukumaran, T.; Laskar, J. M.; Philip, John
2015-02-01
We investigate the effect of hydrodynamic particle size on the magnetic field induced light transmission and transmitted speckle pattern in water based ferrofluids containing functionalized Fe3O4 nanoparticles of size ranging from 15 to 46 nm. Three water-based magnetic nanofluids, containing Fe3O4 nanoparticles functionalized with poly-acrylic acid (PAA), tetra-methyl ammonium hydroxide (TMAOH) and phosphate, are used in the present study. In all three cases, the transmitted light intensity starts decreasing above a certain magnetic field (called first critical field) and becomes a minimum at another field (second critical field). These two critical fields signify the onset of linear aggregation process and zippering transitions between fully grown chains, respectively. Both these critical fields shift towards a lower magnetic field with increasing hydrodynamic diameter, due to stronger magnetic dipolar interactions. The first and the second critical fields showed a power law dependence on the hydrodynamic diameters. The dipolar resonances occurring at certain values of the scatterer size, leads to the field induced extinction of light. Both the onset of chaining and zippering transitions were clearly evident in the time dependent transmitted light intensity. Above the first critical field, the lobe part of the transmitted intensity and the lobe speckle contrast values increase with increasing external magnetic field due to reduced Brownian motion of the field induced aggregates. The speckle contrast was highest for nanoparticle with the largest hydrodynamic diameter, due to reduced Brownian motion. These results provide better insight into field dependent light control in magnetic colloids, which may find interesting applications in magneto-optical devices.
Anisotropy of magnetoviscous effect in structure-forming ferrofluids
NASA Astrophysics Data System (ADS)
Sreekumari, Aparna; Ilg, Patrick
2015-07-01
The magnetoviscous effect, change in viscosity with change in magnetic field strength, and the anisotropy of the magnetoviscous effect, change in viscosity with orientation of magnetic field, have been a focus of interest for four decades. A satisfactory understanding of the microscopic origin of anisotropy of the magnetoviscous effect in magnetic fluids is still a matter of debate and a field of intense research. Here, we present an extensive simulation study to understand the relation between the anisotropy of the magnetoviscous effect and the underlying change in microstructures of ferrofluids. Our results indicate that field-induced chainlike structures respond very differently depending on their orientation relative to the direction of an externally applied shear flow, which leads to a pronounced anisotropy of viscosity. In this work, we focus on three exemplary values of dipolar interaction strengths which correspond to weak, intermediate, and strong interactions between dipolar colloidal particles. We compare our simulation results with an experimental study on cobalt-based ferrofluids as well as with an existing theoretical model called the chain model. A nonmonotonic behavior in the anisotropy of the magnetoviscous effect is observed with increasing dipolar interaction strength and is explained in terms of microstructure formation.
Ferrofluid dynamics in a Hele-Shaw cell simultaneously stressed by DC and rotating magnetic fields
Orji, Uzoma A
2007-01-01
Earlier experiments have been repeated to evaluate magnetic fluid behavior in DC, AC and rotating magnetic fields. Understanding these behaviors are essential to the ferrohydrodynamic applications of ferrofluids in ...
Parallel flow in Hele-Shaw cells with ferrofluids Jos'e A. Miranda
Widom, Michael
Parallel flow in Hele-Shaw cells with ferrofluids Jos'e A Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213 USA (September 14, 1999) Abstract Parallel flow in a Hele-Shaw cell occurs
Snively, Michael John
2011-01-01
The mechanisms that lead to bulk flow within a ferrofluid-filled container subjected to a rotating uniform magnetic field are experimentally studied. There are two prevailing theories: spin diffusion theory and flow due ...
Nonlinear deformation of a ferrofluid droplet in a uniform magnetic field.
Zhu, Gui-Ping; Nguyen, Nam-Trung; Ramanujan, R V; Huang, Xiao-Yang
2011-12-20
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
Graphene oxide/ferrofluid/cement composites for electromagnetic interference shielding application.
Singh, Avanish Pratap; Mishra, Monika; Chandra, Amita; Dhawan, S K
2011-11-18
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
Graphene oxide/ferrofluid/cement composites for electromagnetic interference shielding application
NASA Astrophysics Data System (ADS)
Pratap Singh, Avanish; Mishra, Monika; Chandra, Amita; Dhawan, S. K.
2011-11-01
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.
Recent development of hydrodynamic modeling
NASA Astrophysics Data System (ADS)
Hirano, Tetsufumi
2014-09-01
In this talk, I give an overview of recent development in hydrodynamic modeling of high-energy nuclear collisions. First, I briefly discuss about current situation of hydrodynamic modeling by showing results from the integrated dynamical approach in which Monte-Carlo calculation of initial conditions, quark-gluon fluid dynamics and hadronic cascading are combined. In particular, I focus on rescattering effects of strange hadrons on final observables. Next I highlight three topics in recent development in hydrodynamic modeling. These include (1) medium response to jet propagation in di-jet asymmetric events, (2) causal hydrodynamic fluctuation and its application to Bjorken expansion and (3) chiral magnetic wave from anomalous hydrodynamic simulations. (1) Recent CMS data suggest the existence of QGP response to propagation of jets. To investigate this phenomenon, we solve hydrodynamic equations with source term which exhibits deposition of energy and momentum from jets. We find a large number of low momentum particles are emitted at large angle from jet axis. This gives a novel interpretation of the CMS data. (2) It has been claimed that a matter created even in p-p/p-A collisions may behave like a fluid. However, fluctuation effects would be important in such a small system. We formulate relativistic fluctuating hydrodynamics and apply it to Bjorken expansion. We found the final multiplicity fluctuates around the mean value even if initial condition is fixed. This effect is relatively important in peripheral A-A collisions and p-p/p-A collisions. (3) Anomalous transport of the quark-gluon fluid is predicted when extremely high magnetic field is applied. We investigate this possibility by solving anomalous hydrodynamic equations. We found the difference of the elliptic flow parameter between positive and negative particles appears due to the chiral magnetic wave. Finally, I provide some personal perspective of hydrodynamic modeling of high energy nuclear collisions in the next decade.
Flow of immiscible ferrofluids in a planar gap in a rotating magnetic field
NASA Astrophysics Data System (ADS)
Sule, Bhumika; Torres-Díaz, Isaac; Rinaldi, Carlos
2015-07-01
Analytical solutions are obtained for the steady, fully developed flow of two layers of immiscible ferrofluids of different thicknesses between two parallel plates. Interfacial linear and internal angular momentum balance relations are derived for the case when there is a ferrofluid-ferrofluid interface to obtain the translational and spin velocity profiles in the gap. As expected for the limit of low applied field amplitude, the magnitude of the translational velocity is directly proportional to the frequency of the applied magnetic field and to the square of the magnetic field amplitude. Expressions for the velocity profiles are obtained for the zero spin viscosity and non-zero spin viscosity cases and the effect of applied pressure gradient on the flows is studied. The spin velocity in both ferrofluid phases is in the direction of the rotating magnetic field, except for cases of extreme applied pressure gradients for which the fluid vorticity opposes the spin. We find that for the case of non-zero spin viscosity, flow reversals are predicted using representative ferrofluid property values and field conditions. The unique predictions of the solution with non-zero spin viscosity could be used to experimentally test the existence of couple stresses in ferrofluids and the validity of previously reported values of the so-called spin viscosity.
Three-dimensional x-ray imaging of macro-clusters in ferrofluids
NASA Astrophysics Data System (ADS)
Lee, Wah-Keat
2009-11-01
Ferrofluids are a class of magnetic fluids where nano-sized (˜ 10 nm) magnetic particles are dispersed in a carrier fluid. Ferrofluids have long been used for vacuum seals, but lately, has been proposed for a multitude of new applications including heat transfer and biomedicine. It has been known for some time that the magnetic particles tend to align with an applied magnetic field and that the individual chains can coalesce and form thick and long macro-sized structures whose shapes depend on the properties of the ferrofluid and the applied field. However, due to their opacity to visible light, ferrofluid experiments have been mainly limited to very thin films (˜ 10s of microns). Since the macro-structures can be in the 10-100 micron range, thin film measurements are susceptible to wall effects. TEM and resin techniques have been used to study the structure of these clusters. However, it is doubtful if these frozen or dried structures reflect the natural fluid state. Here, we present x-ray microtomography measurements on a mm-sized tube of ferrofluid under an applied magnetic field. We show the three-dimensional nature of the columns and labyrinth structures. The measurements also allow us to provide estimates on the local magnetic particle concentration within the ferrofluid.
ERIC Educational Resources Information Center
Lafrance, Pierre
1978-01-01
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)
Supersonic flow past bodies in dispersive hydrodynamics
Gurevich, A.V.; Krylov, A.L.; Khodorovskii, V.V.
1995-07-01
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.
Bernhard Mueller; Hans-Thomas Janka; Andreas Marek
2013-03-12
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 (2D) 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 postshock 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 10ms, 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
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.
Neutron spin echo study of low- Tc ferrofluid
NASA Astrophysics Data System (ADS)
Lebedev, V. T.; Gordeev, G. P.; Sibilev, A. I.; Klyubin, V. V.; Torok, Gy.; Cser, L.; Kali, Gy.; Varga, L. K.; Brulet, A.
1999-07-01
We studied the diffusion of single domain particles of Mn 0.3Zn 0.7(Fe 2O 4) ( Rp?100 Å) stabilized by oleic acid in dodecane near the transition temperature Tc of particles from superparamagnetic to paramagnetic state. The structure of the ferrofluid has been studied by small angle neutron scattering. We found a strong density fluctuation near Tc?20°C and H=0, induced by critical spin diffusion. In addition, we studied this system using neutron spin echo (NSE) inelastic scattering. The temperature variation of the self-correlation function G S(T, q, t)= exp[-q 2D (t/?) ?(T)] at momentum transfer q=0.07 Å -1 in the time interval t=0.5-40 ns reveals strong influence of magnetic fluctuations on the mobility: these fluctuations decrease the diffusion rate D and induce stretched relaxation ( ??0.6) at T< Tc?16°C. Above Tc, Stokes diffusion dominates ( ??1)
Photonic Dipole Contours of Ferrofluid Hele-Shaw Cell
Michael Snyder; Jonathan Frederick
2009-03-31
This investigation describes and demonstrates a novel technique for the visualization of magnetic fields. Two ferrofluid Hele-Shaw cells have been constructed to facilitate the imaging of magnetic field lines. We deduce that magnetically induced photonic band gap arrays similar to electrostatic liquid crystal operation are responsible for the photographed images and seek to mathematically prove the images are of dipole nature. A simple way of explaining this work is to think of the old magnetic iron filling experiments; but now each iron filling is a molecule floating in a liquid. Each molecule has the freedom to act as an independent lens that can be aligned by an external magnetic field. Because each lens directs light, the external field can be analyzed by following the light paths captured in the photographs.
Eric Lauga
2015-09-07
Bacteria predate plants and animals by billions of years. Today, they are the world's smallest cells yet they represent the bulk of the world's biomass, and the main reservoir of nutrients for higher organisms. Most bacteria can move on their own, and the majority of motile bacteria are able to swim in viscous fluids using slender helical appendages called flagella. Low-Reynolds-number hydrodynamics is at the heart of the ability of flagella to generate propulsion at the micron scale. In fact, fluid dynamic forces impact many aspects of bacteriology, ranging from the ability of cells to reorient and search their surroundings to their interactions within mechanically and chemically-complex environments. Using hydrodynamics as an organizing framework, we review the biomechanics of bacterial motility and look ahead to future challenges.
Lauga, Eric
2015-01-01
Bacteria predate plants and animals by billions of years. Today, they are the world's smallest cells yet they represent the bulk of the world's biomass, and the main reservoir of nutrients for higher organisms. Most bacteria can move on their own, and the majority of motile bacteria are able to swim in viscous fluids using slender helical appendages called flagella. Low-Reynolds-number hydrodynamics is at the heart of the ability of flagella to generate propulsion at the micron scale. In fact, fluid dynamic forces impact many aspects of bacteriology, ranging from the ability of cells to reorient and search their surroundings to their interactions within mechanically and chemically-complex environments. Using hydrodynamics as an organizing framework, we review the biomechanics of bacterial motility and look ahead to future challenges.
Hydrodynamics of Turning Flocks
Xingbo Yang; M. Cristina Marchetti
2014-10-23
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well polarized flocks. The continuum equations are derived by coarse graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields spin waves that mediate the propagation of turning information throughout the flock. When the inertia is large, we find a novel instability that signals the transition to complex spatio-temporal patterns of continuously turning and swirling flocks.
NASA Astrophysics Data System (ADS)
López, J.; González, Luz E.; Quiñonez, M. F.; Porras-Montenegro, N.; Zambrano, G.; Gómez, M. E.
2014-04-01
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.
Probst, R.; Lin, J.; Komaee, A.; Nacev, A.; Cummins, Z.
2010-01-01
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. PMID:21218157
Probst, R; Lin, J; Komaee, A; Nacev, A; Cummins, Z; Shapiro, B
2011-04-01
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. PMID:21218157
López, J. González, Luz E.; Quiñonez, M. F.; Gómez, M. E.; Porras-Montenegro, N.; Zambrano, G.
2014-05-21
Ferrofluids based on magnetic Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} ferrite nanoparticles were prepared by co-precipitation method from aqueous salt solutions of Co (II), ZnSO{sub 4}, 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 Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} 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.
Interfacial stress balances in structured continua and free surface flows in ferrofluids
Chaves, Arlex [School of Chemical Engineering, Universidad Industrial de Santander, Calle 9 Cra. 27, Edificio 24, Bucaramanga, Santander (Colombia)] [School of Chemical Engineering, Universidad Industrial de Santander, Calle 9 Cra. 27, Edificio 24, Bucaramanga, Santander (Colombia); Rinaldi, Carlos, E-mail: carlos.rinaldi@bme.ufl.edu [J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32611, USA and Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611 (United States)] [J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32611, USA and Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611 (United States)
2014-04-15
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.
Carlos Hoyos; Bom Soo Kim; Yaron Oz
2014-02-09
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. Scaling arguments fix the resistivity to be linear in the temperature.
NASA Astrophysics Data System (ADS)
Lopez, Javier; Gonzalez, Luz Esther; Quinonez, Mario; Porras, Nelson; Zambrano, Gustavo; Gomez, Maria Elena
2014-03-01
Using a ferrfluid of cobalt-zinc ferrite nanoparticles Co(1 - x)ZnxFe2O4 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. Departamento de Física, Universidad del Valle, A.A. 25360, Cali, Colombia
Optical properties in one-dimensional graded soft photonic crystals with ferrofluids
NASA Astrophysics Data System (ADS)
Fan, Chunzhen; Wang, Junqiao; Zhu, Shuangmei; He, Jinna; Ding, Pei; Liang, Erjun
2013-05-01
We theoretically investigate the optical properties in one-dimensional graded soft photonic crystals (1D GSPCs). The proposed structure is constituted of the stacked ferrofluids layer and the dielectric layer. Due to the supermagnetic response of the ferromagnetic nanoparticles, they will align in a line under the influence of the initiated magnetic field, thereby modulating the refractive index of the ferrofluids layer. By resorting to the transfer matrix method, the dispersion relation, transmittance and reflectance in 1D GSPCs were calculated. Numerical results show that a broad photonic band gap appears in such systems, which can even be broadened by increasing the volume fraction of ferromagnetic nanoparticles. Moreover, perfect transmittance of our proposed structure can be realized with an increased number of ferrofluid layers. In comparison with conventional PCs materials, 1D GSPCs composed of liquid material offer a very flexible route to implementation, which can be widely used in the application of optical filters, waveguides, reflectors and so on.
Paul, Nibedita; Devi, Manasi; Mohanta, Dambarudhar; Saha, Abhijit
2012-02-15
The present work reports on magnetically induced optical activity (such as Faraday rotation and linear dichroism) of pristine and gamma-irradiated gadolinium oxide (Gd{sub 2}O{sub 3}) nanoparticle-based ferrofluids. The ferrofluids were produced by dispersing N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB)-coated {approx}9-nm-sized Gd{sub 2}O{sub 3} particles in a carrier fluid of ethanol. The ferrofluids were then irradiated with 1.25 MeV energetic gamma rays (dose: 868 Gy and 2.635 kGy). Irradiation-led formation of a number of point defects was revealed through high resolution electron microscopy. The interaction of light with the ionized point defects is believed to have caused substantial improvement in the magneto-optic response of irradiated magnetic fluids.
Simulation of the magnetization dynamics of diluted ferrofluids in medical applications.
Rogge, Henrik; Erbe, Marlitt; Buzug, Thorsten M; Lüdtke-Buzug, Kerstin
2013-12-01
Ferrofluids, which are stable, colloidal suspensions of single-domain magnetic nanoparticles, have a large impact on medical technologies like magnetic particle imaging (MPI), magnetic resonance imaging (MRI) and hyperthermia. Here, computer simulations promise to improve our understanding of the versatile magnetization dynamics of diluted ferrofluids. A detailed algorithmic introduction into the simulation of diluted ferrofluids will be presented. The algorithm is based on Langevin equations and resolves the internal and the external rotation of the magnetic moment of the nanoparticles, i.e., the Néel and Brown diffusion. The derived set of stochastic differential equations are solved by a combination of an Euler and a Heun integrator and tested with respect to Boltzmann statistics. PMID:24163220
NASA Astrophysics Data System (ADS)
Paul, Nibedita; Devi, Manasi; Mohanta, Dambarudhar; Saha, Abhijit
2012-02-01
The present work reports on magnetically induced optical activity (such as Faraday rotation and linear dichroism) of pristine and gamma-irradiated gadolinium oxide (Gd2O3) nanoparticle-based ferrofluids. The ferrofluids were produced by dispersing N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB)-coated ˜9-nm-sized Gd2O3 particles in a carrier fluid of ethanol. The ferrofluids were then irradiated with 1.25 MeV energetic gamma rays (dose: 868 Gy and 2.635 kGy). Irradiation-led formation of a number of point defects was revealed through high resolution electron microscopy. The interaction of light with the ionized point defects is believed to have caused substantial improvement in the magneto-optic response of irradiated magnetic fluids.
Dielectric response of transformer oil based ferrofluid in low frequency range
NASA Astrophysics Data System (ADS)
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
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.
Mössbauer effect and magnetism of single domain Fe3O4 particles in ferrofluids
NASA Astrophysics Data System (ADS)
Tari, A.; Popplewell, J.; Charles, S. W.; Bunbury, D. St. P.; Alves, K. M. B.
1983-06-01
Three ferrofluids, consisting of suspensions of Fe3O4 particles of ?100-200 Å diameter in diester, hydrocarbon, and water have been investigated at temperatures 4.2-300 K by means of Mössbauer effect and magnetic measurements. The magnetic data displays almost all the features observed in the spin glasses. The Néel model is used to explain the behavior of the fluids. From the temperature variation of the initial susceptibility and the isothermal remanence, K=(3.5±0.7)×105 erg/cc and D0=(80±5) Å are obtained for the anisotropy constant and the median diameter, respectively, of the diester based ferrofluid. The ac susceptibility gives K=3×105 erg/cc and D0=92 Å. For the water based ferrofluid measurements give K=1.5×105 erg/cc. Values obtained from Mössbauer measurements for K and D0 agree with those obtained from magnetization-susceptibility data.
Colgate, S.A.
1981-01-01
The explosion of a star supernova occurs at the end of its evolution when the nuclear fuel in its core is almost, or completely, consumed. The star may explode due to a small residual thermonuclear detonation, type I SN or it may collapse, type I and type II SN leaving a neutron star remnant. The type I progenitor should be thought to be an old accreting white dwarf, 1.4 M/sub theta/, with a close companion star. A type II SN is thought to be a massive young star 6 to 10 M/sub theta/. The mechanism of explosion is still a challenge to our ability to model the most extreme conditions of matter and hydrodynamics that occur presently and excessively in the universe. 39 references.
Mössbauer spectroscopy and magnetic studies of orientated textured Fe3O4 ferrofluid
NASA Astrophysics Data System (ADS)
Gadhvi, Mrudul; Srivastava, S.; Kurian, Sajith; Gajbhiye, N. S.
2009-01-01
Nano scale magnetite based ferrofluid is synthesized by chemical co pre cipitation technique and stabilized with oleic acid. Magnetization and viscosity measurements were used to optimize for texturing purpose. The freeze-textured ferrofluid in two configurations, namely, (1) field texture system (FTS) and (2) zero field texture system (ZTS) are investigated by magnetization measurements at 298 K and Mössbauer spectroscopy measurements at 77 and 298 K. These results are analysed on the basis of the contributions from collective superparamagnetic reversal and the strength of the inter particle interactions.
Moridis, G.J.; Borglin, S.E.; Oldenburg, C.M.; Becker, A.
1998-03-01
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.
Stable ferrofluids of magnetite nanoparticles in hydrophobic ionic liquids.
Mestrom, Luuk; Lenders, Jos J M; de Groot, Rick; Hooghoudt, Tonnis; Sommerdijk, Nico A J M; Artigas, Marcel Vilaplana
2015-07-17
Ferrofluids (FFs) of metal oxide nanoparticles in ionic liquids (ILs) are a potentially useful class of magnetic materials for many applications because of their properties related to temperature/pressure stability, hydrophobicity, viscosity and recyclability. In this work, the screening of several designer surfactants for their stabilizing capabilities has resulted in the synthesis of stable FFs of superparamagnetic 7 ± 2 nm magnetite (Fe3O4) nanoparticles in the hydrophobic IL 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(R)MIM][NTf2]). The designed and synthesized 1-butyl-3-(10-carboxydecyl)-1H-imidazol-3-ium bromide (ILC10-COOH) surfactant that combines the same imidazole moiety as the IL with a long alkyl chain ensured compatibility with the IL and increased the steric repulsion between the magnetite nanoparticles sufficiently such that stable dispersions of up to 50 wt% magnetite were obtained according to stability tests in the presence of a magnetic field (0.5-1 Tesla). Cryo-transmission electron microscopy (cryo-TEM) of the IL-based FFs allowed direct visualization of the surfactant-stabilized nanoparticles in the ILs and the native, hardly aggregated state of their dispersion. PMID:26118409
Negative Refractive Index in Hydrodynamical Systems
Antonio Amariti; Davide Forcella; Alberto Mariotti
2011-07-06
We discuss the presence of exotic electromagnetic phenomena in systems with finite charge density which are described by hydrodynamics. We show that such systems generically have negative refractive index for low frequency electromagnetic waves, i.e. the energy flux and the phase velocity of the wave propagate in opposite directions. We comment on possible phenomenological applications, focusing on the Quark Gluon Plasma.
Perspectives in coral reef hydrodynamics
NASA Astrophysics Data System (ADS)
Hearn, Clifford J.
2011-06-01
Some developments in coral reef hydrodynamics over the last decade are reviewed with an overview of papers in this special issue. Advances in hydrodynamics based on improved understanding of topographic complexity are illustrated for the reef at Kilo Nalu Observatory and Kaneohe Bay (both in Hawaii). Models of the roughness layer are discussed as a background to numerical models of reef hydrodynamics for Molokai and Guam. Topographic complexity produces spatial temperature variability over reefs creating thermal microclimates which are reported in this issue for the Red Sea. Uptake of ocean nutrients by reefs is controlled by hydrodynamics, and papers in this issue show its critical role in the ecology of a fringing reef at La Réunion Island; nutrient uptake rates are discussed here using new data for Hearn Roughness and Decadal Rugosity. The role of upwelled water by large amplitude internal waves on reefs is reported for the Similan Islands, providing major new evidence for the role of hydrodynamics in the ecology of reefs and its importance to climate change. The review suggests some important areas for new research including simulated corals used in flumes and the field. Major new modeling based on measured roughness maps combined with small scale lattice Boltzmann simulations should be possible in the next decade.
Hydrodynamic Flow from Fast Particles
Casalderrey-Solana, J; Teaney, D
2006-01-01
We study the hydrodynamical response of the quark gluon plasma to the passage of high momentum particle within the context of linearized hydrodynamics in a static fluid. Two modes can be excited, the sound and the diffuson. Assuming that significant part of the energy lost by the particle thermalizes we discuss the modification of the azimuthal dihadron distributions due to the jet induced flow (conical flow). If the energy loss is large and no significant entropy is produced, large angle correlations are produced at Df =p ?1.2rad. We also estimate the effect of the expanding fireball on the sound wave amplitude, which grows as a consequence of the dilution of the background medium. Finally, if the speed of sound goes to zero at the mixed phase (first order phase transition) reflected waves appear that lead to correlation at Df = 1.4rad.
Waves in Radial Gravity Using Magnetic Fluid
NASA Technical Reports Server (NTRS)
Ohlsen, D. R.; Hart, J. E.; Weidman, P. D.
1999-01-01
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
King, Lyon B.
-droplet direct writing onto surfaces,12 and as micro-scale ion thrusters for spacecraft propulsion.13 values. Many technological applications of electrospray could be improved by increasing the spray ferrofluid surface instabilities and jets Lyon B. King* Michigan Technological University, Houghton, MI
Under consideration for publication in J. Fluid Mech. 1 Field-induced motion of ferrofluid droplets
Renardy, Yuriko
system is investigated in Mefford et al. (2007) with a ferrofluid drop, assumed to be a solid sphere, momentum equation and incompressibility. A numerical algorithm is derived to model the interface between-surface-force formulation is used to model the interfacial tension force as a body force, and the placement of the liquids
Superparamagnetic amorphous Fe1- x C x alloy particles in a ferrofluid
NASA Astrophysics Data System (ADS)
Mørup, S.; Bødker, F.; van Wonterghem, J.; Madsen, M. B.; Bentzon, M. D.
1989-06-01
A ferrofluid with ultrasmall magnetic particles ( d?3.3 nm) of amorphous Fe1- x C x has been studied by Mössbauer spectroscopy and electron microscopy. The values of the particle size estimated by the two methods are in good agreement. The magnetic anisotropy energy constant, K=(1.0±0.3)×105 J m-3 has been estimated.
Two-Dimensional Melting of a Crystal of Ferrofluid Spikes Francois Boyer1
Falcon, Eric
driven by a magnetic field gradient, magnetic levitation, labyrinthine and Rosensweig instabilities [18 thin colloidal suspensions [11,12], liquid films [13], vibrated granular monolayers [14,15], magnetic]. This latter occurs when a normal static magnetic field applied to a pool of ferrofluid exceeds a critical
Optimization of ferrofluid motion on solid substrate and its application to micro-mirror device
NASA Astrophysics Data System (ADS)
Yu, Seonuk; Kim, Dongil; Cho, Il-Joo; Yun, Kwang-Seok
2015-06-01
This paper presents and demonstrates the optimization of an oil-based ferrofluid droplet on a solid surface and its application to a micro-mirror device with a fast switching time. The motion of the ferrofluid droplet on a hydrophilic surface was examined at various surfactant concentrations for both rotational and linear reciprocating actuations. A maximum moving speed of 0.733 m/s was measured at a poly(vinyl alcohol) (PVA) concentration of 0.1 wt % during the rotational motion of the ferrofluid droplet. In addition, a fast reciprocating motion was successfully demonstrated during the linear operation experiment without droplet separation or surface contamination. A maximum acceleration and deceleration of 28 m/s2 was measured at a PVA concentration of 0.1 wt %. As an application of the fast motion of the ferrofluid, a current-driven micro-mirror was proposed and experimentally demonstrated. Switching times of 25 and 18 ms were measured for the closing and opening phases of the mirror, respectively.
NASA Astrophysics Data System (ADS)
Butter, K.; Bomans, P. H.; Frederik, P. M.; Vroege, G. J.; Philipse, A. P.
2003-04-01
The particle structure of ferrofluids is studied in situ, by cryogenic electron microscopy, on vitrified films of iron and magnetite dispersions. By means of synthesis of iron colloids with controlled particle size and different types of surfactant, dipolar particle interactions can be varied over a broad range, which significantly influences the ferrofluid particle structure. Our experiments on iron dispersions (in contrast to magnetite dispersions) for the first time demonstrate, in ferrofluids in zero field, a transition with increasing particle size from separate particles to linear chains of particles (Butter K, Bomans P H, Frederik P M, Vroege G J and Philipse A P 2003 Nature Mater. 2 88). These chains, already predicted theoretically by de Gennes and Pincus (de Gennes P G and Pincus P A 1970 Phys. Kondens. Mater. 11 189), very much resemble the fluctuating chains found in simulations of dipolar fluids (Weis J J 1998 Mol. Phys. 93 361, Chantrell R W, Bradbury A, Popplewell J and Charles S W 1982 J. Appl. Phys. 53 2742). Decreasing the range of steric repulsion between particles by employing a thinner surfactant layer is found to change particle structures as well. The dipolar nature of the aggregation is confirmed by the alignment of existing chains and individual particles in the field direction upon vitrification of dispersions in a saturating magnetic field. Frequency-dependent susceptibility measurements indicate that particle structures in truly three-dimensional ferrofluids are qualitatively similar to those in liquid films.
Thermal conductivity measurements on ferrofluids containing metallic cobalt and iron particles
NASA Astrophysics Data System (ADS)
Popplewell, J.; Al-Qenaie, A.
1987-03-01
The thermal conductivity of ferrofluids containing cobalt or iron particles dispersed in toluene or hydrocarbon oil carriers has been measured for different particle concentrations. The concentration dependence of the thermal conductivity found experimentally is well described by Tareef's equation for solid/liquid mixtures.
Hydrodynamics of rotating superfluids
Chandler, E.A.
1981-01-01
In this thesis, a coarse grained hydrodynamics is developed from the exact description of Tkachenko. To account for the dynamics of the vortex lattice, the macroscopic vortex displacement field is treated as an independent degree of freedom. The conserved energy is written in terms of the coarse-grained normal fluid, superfluid, and vortex velocities and includes an elastic energy associated with deformations of the vortex lattice. Equations of motion consistent with the conservation of energy, entropy and vorticity and containing mutual friction terms arising from microscopic interactions between normal fluid excitations and the vortex lines are derived. When the vortex velocity is eliminated from the damping terms, this system of equations becomes essentially that of BK with added elastic terms in the momentum stress tensor and energy current. The dispersion relation and damping of the first and second sound modes and the two transverse modes sustained by the system are investigated. It is shown that mutual friction mixes the transverse modes of the normal and superfluid components and damps the transverse mode associated with the relative velocity of these components, making this wave evanescent in the plane perpendicular to the rotation axis. The wave associated with transverse motion of the total mass current is a generalized Tkachenko mode, whose dispersion relation reduces to that derived by Tkachenko wave when the wavevector lies in this plane.
Bruinsma, Robijn; Grosberg, Alexander Y.; Rabin, Yitzhak; Zidovska, Alexandra
2014-01-01
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
Hydrodynamics of Turning Flocks
NASA Astrophysics Data System (ADS)
Yang, Xingbo; Marchetti, M. Cristina
2015-03-01
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well polarized flocks. The continuum equations are derived by coarse graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields spin waves that mediate the propagation of turning information throughout the flock. When the inertia is large, we find a novel instability that signals the transition to complex spatio-temporal patterns of continuously turning and swirling flocks. This work was supported by the NSF Awards DMR-1305184 and DGE-1068780 at Syracuse University and NSF Award PHY11-25915 and the Gordon and Betty Moore Foundation Grant No. 2919 at the KITP at the University of California, Santa Barbara.
Direct observations of field-induced assemblies in magnetite ferrofluids
NASA Astrophysics Data System (ADS)
Mousavi, N. S. Susan; Khapli, Sachin D.; Kumar, Sunil
2015-03-01
Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ? 10 nm) is studied with an emphasis on examining the effects of particle concentration (?) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ? = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05-0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.
Soto-Aquino, D; Rosso, D; Rinaldi, C
2011-11-01
Ferrofluids are colloidal suspensions of magnetic nanoparticles that exhibit normal liquid behavior in the absence of magnetic fields but respond to imposed magnetic fields by changing their viscosity without loss of fluidity. The response of ferrofluids to constant shear and magnetic fields has received a lot of attention, but the response of ferrofluids to oscillatory shear remains largely unexplored. In the present work we used rotational Brownian dynamics to study the dynamic properties of ferrofluids with thermally blocked nanoparticles under oscillatory shear and constant magnetic fields. Comparisons between simulations and modeling using the ferrohydrodynamics equations were also made. Simulation results show that, for small rotational Péclet number, the in-phase and out-of-phase components of the complex viscosity depend on the magnitude of the magnetic field and frequency of the shear, following a Maxwell-like model with field-dependent viscosity and characteristic time equal to the field-dependent transverse magnetic relaxation time of the nanoparticles. Comparison between simulations and the numerical solution of the ferrohydrodynamic equations shows that the oscillatory rotational magnetoviscosity for an oscillating shear field obtained using the kinetic magnetization relaxation equation quantitatively agrees with simulations for a wide range of Péclet number and Langevin parameter but has quantitative deviations from the simulations at high values of the Langevin parameter. These predictions indicate an apparent elastic character to the rheology of these suspensions, even though we are considering the infinitely dilute limit in which there are negligible particle-particle interactions and, as such, chains do not form. Additionally, an asymptotic analytical solution of the ferrohydrodynamics equations, valid for Pe<2, was used to demonstrate that the Cox-Merz rule applies for dilute ferrofluids under conditions of small shear rates. At higher shear rates the Cox-Merz rule ceases to apply. PMID:22181497
V. Socoliuc; L. B. Popescu
2014-10-09
An analytical theoretical model for the influence of the magnetically induced nanoparticle chaining on the linear dichroism in ferrofluids was developed. The model is based on a statistical theory for magnetic nanoparticle chaining in ferrofluids. Together with appropriate experimental approach and data processing strategy, the model grounds a magneto-optical granulometry method able to determine the magnetic field dependence of the statistics of magnetically induced particle chains in concentrated ferrofluids.
Algorithm refinement for fluctuating hydrodynamics
Williams, Sarah A.; Bell, John B.; Garcia, Alejandro L.
2007-07-03
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.
NASA Astrophysics Data System (ADS)
Cherief, Wahid; Avenas, Yvan; Ferrouillat, Sébastien; Kedous-Lebouc, Afef; Jossic, Laurent; Berard, Jean; Petit, Mickael
2015-07-01
Applying a magnetic field on a ferrofluid flow induces a large increase of the convective heat transfer coefficient. In this paper, the thermal-hydraulic behaviors of two commercial ferrofluids are compared. The variations of both the pressure drop and the heat transfer coefficient due to the magnetic field are measured in the following conditions: square duct, laminar flow and uniform wall heat flux. The square section with two insulated walls allows for the characterization of the effect of the magnetic field direction. The experimental results show that the heat transfer is better enhanced when the magnetic field is perpendicular to the heat flux. In the best case, the local heat transfer coefficient increase is about 75%. On the contrary, another experimental setup shows no enhancement of thermal conductivity when the magnetic field is perpendicular to the heat flux. Contribution to the topical issue "Electrical Engineering Symposium (SGE 2014) - Elected submissions", edited by Adel Razek
Programmable two-dimensional actuation of ferrofluid droplet using planar microcoils
NASA Astrophysics Data System (ADS)
Beyzavi, Ali; Nguyen, Nam-Trung
2010-01-01
This paper reports the concept and the device for two-dimensional magnetic actuation of a ferrofluid droplet. Four planar microcoils were etched on one side of a printed circuit board (PCB). The magnetic field was digitally controlled by adjusting the magnitude and the polarity of the driving current in the coils. A computer programme generates the control signals, which are conditioned by an external amplifier circuit and transferred to the coils. The ferrofluid droplet is attracted to the field maximum. With the controlled magnetic field, the location of the field maximum can be changed electronically allowing the droplet to move in a closed loop on the planar platform. The concept presented in this paper can have a variety of applications in digital microfluidics such as sample transport or mixing.
Active surfaces: Ferrofluid-impregnated surfaces for active manipulation of droplets
NASA Astrophysics Data System (ADS)
Khalil, Karim S.; Mahmoudi, Seyed Reza; Abu-dheir, Numan; Varanasi, Kripa K.
2014-07-01
Droplet manipulation and mobility on non-wetting surfaces is of practical importance for diverse applications ranging from micro-fluidic devices, anti-icing, dropwise condensation, and biomedical devices. The use of active external fields has been explored via electric, acoustic, and vibrational, yet moving highly conductive and viscous fluids remains a challenge. Magnetic fields have been used for droplet manipulation; however, usually, the fluid is functionalized to be magnetic, and requires enormous fields of superconducting magnets when transitioning to diamagnetic materials such as water. Here we present a class of active surfaces by stably impregnating active fluids such as ferrofluids into a textured surface. Droplets on such ferrofluid-impregnated surfaces have extremely low hysteresis and high mobility such that they can be propelled by applying relatively low magnetic fields. Our surface is able to manipulate a variety of materials including diamagnetic, conductive and highly viscous fluids, and additionally solid particles.
Transient magneto-optic effects in ferrofluid-filled microstructured fibers in pulsed magnetic field
NASA Astrophysics Data System (ADS)
Agruzov, Petr M.; Pleshakov, Ivan V.; Bibik, Efim E.; Stepanov, Serguei I.; Shamrai, Alexander V.
2015-09-01
Transient magneto-optic effects in ferrofluid-filled microstructured optical fibers are considered. Magneto-optic responses of two types, i.e., an even and an odd one, were observed in the longitudinal geometry of an applied pulsed magnetic field for the kerosene-based Fe3O4 ferrofluid with ?8 \\text{nm} nanoparticles. For the first time a submicrosecond response time limited by the rise time of the applied field pulse (?0.35 ? \\text{s}) was demonstrated for the odd magneto-optic effect in an all-fiber system, and responses of the even and odd magneto-optic effects were separated. A strong influence of the pulse width on the relaxation time of the even response is attributed to the formation of particle aggregates.
Modeling of retardance in ferrofluid with Taguchi-based multiple regression analysis
NASA Astrophysics Data System (ADS)
Lin, Jing-Fung; Wu, Jyh-Shyang; Sheu, Jer-Jia
2015-03-01
The citric acid (CA) coated Fe3O4 ferrofluids are prepared by a co-precipitation method and the magneto-optical retardance property is measured by a Stokes polarimeter. Optimization and multiple regression of retardance in ferrofluids are executed by combining Taguchi method and Excel. From the nine tests for four parameters, including pH of suspension, molar ratio of CA to Fe3O4, volume of CA, and coating temperature, influence sequence and excellent program are found. Multiple regression analysis and F-test on the significance of regression equation are performed. It is found that the model F value is much larger than Fcritical and significance level P <0.0001. So it can be concluded that the regression model has statistically significant predictive ability. Substituting excellent program into equation, retardance is obtained as 32.703°, higher than the highest value in tests by 11.4%.
Temperature Dependence of Particle Size Distribution in Transformer Oil-Based Ferrofluid
NASA Astrophysics Data System (ADS)
Józefczak, Arkadiusz; Hornowski, Tomasz; Skumiel, Andrzej
2011-04-01
The temperature dependence of the particle size distribution (PSD) of a transformer oil-based ferrofluid was studied using an ultrasound method. The measurements of the ultrasound velocity and attenuation were carried out in the absence of an external magnetic field as a function of the volume concentration of magnetite particles at temperatures ranging from 10 °C to 80 °C. The experimental results of ultrasound measurements were analyzed within the framework of the Vinogradov-Isakovich theory which takes into account contributions to acoustical parameters due to friction and heat exchange between magnetic particles and the surrounding carrier liquid. From the best fit of the experimental results and theoretical predictions, the parameters characterizing the PSD at different temperatures were determined. In order to analyze ultrasonic data, the density and viscosity of ferrofluid samples and the transformer oil were also measured.
Rheological investigations on the theoretical predicted “Poisoning” effect in bidisperse ferrofluids
NASA Astrophysics Data System (ADS)
Siebert, E.; Dupuis, V.; Neveu, S.; Odenbach, S.
2015-01-01
Interparticle interactions in ferrofluids especially the influence of small particles on the agglomeration behaviour of large particles were the topic of numerous theoretical predictions and simulations as well as of experimental investigations. In this context the "Poisoning" effect describes the decrease of the magnetoviscous effect in the presence of small particles in a bidisperse model fluid. In order to examine this effect rheological experiments have been carried out by means of a specially designed rheometer, which allows measurements under the influence of an applied magnetic field. We were able to synthesize ferrofluids with a narrow particle size distribution containing only small or large cobalt ferrite nanoparticles, which were mixed to receive various bidisperse fluid samples. With these fluids changes of the viscous behaviour in a magnetic field have been measured and compared according to their individual compositions.
Synthesis and characterization of size-controlled cobalt-ferrite-based ionic ferrofluids
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
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.
ON THE INSTABILITY OF SOLITONS IN SHEAR HYDRODYNAMIC FLOWS
ON THE INSTABILITY OF SOLITONS IN SHEAR HYDRODYNAMIC FLOWS Sergey K. Zhdanov Plasma Physics. The instability region and the short-wave instability threshold for plane solitons are found nu- merically-focusing instability; Two-dimensional long-wave models. 3 #12;1 INTRODUCTION Stability of non-linear waves in various
LaCure, Mari Mae
2010-04-29
Waves is the supporting document to the Master of Fine Arts thesis exhibition of the same title. Exhibited March 7-12 2010 in the Art and Design Gallery at the University of Kansas, Waves was comprised of a series of mixed media drawings...
Three-dimensional hydrodynamic hot-spot
Mader, C.L.
1984-01-01
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.
Investigation of the effect of magnetic field on ferrofluid in microelectromechanical devices (MEMS)
NASA Astrophysics Data System (ADS)
Lee, Ann; Yeoh, Guan H.; Lim, Shen H.; Prusty, B. Gangadhara
2013-08-01
Considerable efforts have been spent in the development of magnetic nanoparticles (MNPs) in the last decade to understand their behaviour, and the improvement of their applicability in many different areas. Precise control over the synthesis conditions and surface functionalization of MNPs is crucial because it governs their physical properties and their colloidal stability. The magnetic platforms possess very small size and narrow size distribution together with high magnetization values. These nanoparticles (NPs) must combine high magnetic susceptibility for an optimum magnetic enrichment and loss of magnetization after removal of the magnetic field. Computational Fluid Dynamics (CFD) approach has been used to investigate the impact of a magnetic field in ferrofluid flow through a T-microchannel. The microchannel consists of one 400?m wide main branch and two 200?m wide sidebranches. Available experimental data is used to validate the Eulerian-Eulerian approach in simulating the nanoparticles in flow flow under the influence of magnetic field. In general, magnetic nanoparticles are deflected across the suspending ferrofluid by negative magnetophoresis and confined by a water flow to the center of the micro-channel. The effect of ferrofluid flow rate on the particle focusing performance has been examined. It is found that the particle focusing effectiveness increases with decreasing flow rate.
Zhou, Yilong; Kumar, Dhileep Thanjavur; Lu, Xinyu; Kale, Akshay; DuBose, John; Song, Yongxin; Wang, Junsheng; Li, Dongqing; Xuan, Xiangchun
2015-07-01
Trapping and preconcentrating particles and cells for enhanced detection and analysis are often essential in many chemical and biological applications. Existing methods for diamagnetic particle trapping require the placement of one or multiple pairs of magnets nearby the particle flowing channel. The strong attractive or repulsive force between the magnets makes it difficult to align and place them close enough to the channel, which not only complicates the device fabrication but also restricts the particle trapping performance. This work demonstrates for the first time the use of a single permanent magnet to simultaneously trap diamagnetic and magnetic particles in ferrofluid flows through a T-shaped microchannel. The two types of particles are preconcentrated to distinct locations of the T-junction due to the induced negative and positive magnetophoretic motions, respectively. Moreover, they can be sequentially released from their respective trapping spots by simply increasing the ferrofluid flow rate. In addition, a three-dimensional numerical model is developed, which predicts with a reasonable agreement the trajectories of diamagnetic and magnetic particles as well as the buildup of ferrofluid nanoparticles. PMID:26221197
A method for measuring the Néel relaxation time in a frozen ferrofluid
NASA Astrophysics Data System (ADS)
Tackett, Ronald J.; Thakur, Jagdish; Mosher, Nathaniel; Perkins-Harbin, Emily; Kumon, Ronald E.; Wang, Lihua; Rablau, Corneliu; Vaishnava, Prem P.
2015-08-01
We report a novel method of determining the average Néel relaxation time and its temperature dependence by calculating derivatives of the measured time dependence of temperature for a frozen ferrofluid exposed to an alternating magnetic field. The ferrofluid, composed of dextran-coated Fe3O4 nanoparticles (diameter 13.7 nm ± 4.7 nm), was synthesized via wet chemical precipitation and characterized by x-ray diffraction and transmission electron microscopy. An alternating magnetic field of constant amplitude ( H 0 = 20 kA/m) driven at frequencies of 171 kHz, 232 kHz, and 343 kHz was used to determine the temperature dependent magnetic energy absorption rate in the temperature range from 160 K to 210 K. We found that the specific absorption rate of the ferrofluid decreased monotonically with temperature over this range at the given frequencies. From these measured data, we determined the temperature dependence of the Néel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of 40 kJ/m3, in agreement with previously published results.
Optical and rheological study of gamma irradiated rare-earth nanoparticle based ferrofluids
NASA Astrophysics Data System (ADS)
Paul, Nibedita; Mohanta, Dambarudhar; Saha, Abhijit
2012-12-01
The present work reports on the optical and rheological properties of unexposed and gamma irradiated rare-earth (RE) oxide nanoparticle-based ferrofluids (FF). The ferrofluids were prepared by dispersing surfactant coated gadolinium oxide (Gd2O3) nanoparticles in ethanol medium and later on subjected to energetic gamma irradiation (1.25 MeV) at select doses. As predicted from transmission electron microscopy and X-ray diffraction (XRD) studies, the synthesized nanoparticles are of ˜7 nm size which crystallize into cubic crystal structure. The photoluminescence response reveals creation of defect states on nanoparticle surfaces when FFs are subjected to gamma irradiation. Whereas, rheology measurements showed unusual shear thinning behavior of the ferrofluids. The flow behavior of all the samples can be correlated to the bi-exponential decay curve fitting which reveals that decay phenomenon is governed by two independent mechanism: fast and slow events. The variation of the decay parameter with irradiation dose is attributed to the creation of point defects and weakening of inter nanoparticle bonding.
NASA Astrophysics Data System (ADS)
Alexiou, Ch.; Schmid, R.; Jurgons, R.; et al.
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.
Hydrodynamic obstruction to bubble expansion
Konstandin, Thomas [CERN Physics Department, Theory Division, CH-1211 Geneva 23 (Switzerland); No, José M., E-mail: tkonstan@cern.ch, E-mail: jose-miguel.no@cea.fr [Institut de Physique Théorique, CEA/Saclay, F-91191 Gif-sur-Yvette Cédex (France)
2011-02-01
We discuss a hydrodynamic obstruction to bubble wall acceleration during a cosmological first-order phase transition. The obstruction results from the heating of the plasma in the compression wave in front of the phase transition boundary. We provide a simple criterion for the occurrence of the obstruction at subsonic bubble wall velocity in terms of the critical temperature, the phase transition temperature, and the latent heat of the model under consideration. The criterion serves as a sufficient condition of subsonic bubble wall velocities as required by electroweak baryogenesis.
Ergoregion instability: The hydrodynamic vortex
Leandro A. Oliveira; Vitor Cardoso; Luís C. B. Crispino
2014-05-16
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 which can be realized in the laboratory: the {\\it hydrodynamic vortex}, an effective geometry for sound waves, with ergoregion and without an event horizon.
1. Department, course number, title ORE 609 Hydrodynamics of Fluid-Body Interaction
with prescribed body motion, fixed and freely floating bodies. 4. Prerequisites Water-Wave Theories (ORE 6071. Department, course number, title ORE 609 Hydrodynamics of Fluid-Body Interaction 2. Designation of Fluid-Body Interaction. (3) Hydrodynamics of ships, coastal and offshore structures. Wave forces
Extinction of polarized light in ferrofluids with different magnetic particle concentrations
NASA Astrophysics Data System (ADS)
Socoliuc, V.; Popescu, L. B.
2012-01-01
The magnetic field intensity and nanoparticle concentration dependence of the polarized light extinction in a ferrofluid made of magnetite particles stabilized with technical grade oleic acid dispersed in transformer oil was experimentally investigated. The magnetically induced optical anisotropy, i.e. the dichroism divided by concentration, was found to decrease with increasing sample concentration from 2% to 8%. The magnetically induced change in the optical extinction of light polarized at 54.74° with respect to the magnetic field direction was found to be positive for the less concentrated sample (2%) and negative for the samples with 4% and 8% magnetic nanoparticle concentrations, the more negative the higher the concentration and field intensity. Based on the theoretically proven fact [11] that the particle orientation mechanism has no effect on the extinction of light polarized at 54.74° with respect to the field direction, we analyzed the experimental findings in the frames of the agglomeration and long-range pair correlations theories for the magnetically induced optical anisotropy in ferrofluids. We developed a theoretical model in the approximation of single scattering for the optical extinction coefficient of a ferrofluid with magnetically induced particle agglomeration. The model predicts the existence of a polarization independent component of the optical extinction coefficient that is experimentally measurable at 54.74° polarization angle. The change in the optical extinction of light polarized at 54.74° is positive if only the formation of straight n-particle chains is considered and may become negative in the hypothesis that the longer chains degenerate to more isotropic structures (polymer-like coils, globules or bundles of chains). The model for the influence on the light absorption of the long-range pair correlations, published elsewhere, predicts that the change in the optical extinction of light polarized at 54.74° is always negative, the more negative the higher the magnetic field intensity and particle concentration.
Hydrodynamics of the Chiral Dirac Spectrum
Liu, Yizhuang; Zahed, Ismail
2015-01-01
We derive a hydrodynamical description of the eigenvalues of the chiral Dirac spectrum in the vacuum and in the large $N$ (volume) limit. The linearized hydrodynamics supports sound waves. The stochastic relaxation of the eigenvalues is captured by a hydrodynamical instanton configuration which follows from a pertinent form of Euler equation. The relaxation from a phase of localized eigenvalues and unbroken chiral symmetry to a phase of de-localized eigenvalues and broken chiral symmetry occurs over a time set by the speed of sound. We show that the time is $\\Delta \\tau=\\pi\\rho(0)/2\\beta N$ with $\\rho(0)$ the spectral density at zero virtuality and $\\beta=1,2,4$ for the three Dyson ensembles that characterize QCD with different quark representations in the ergodic regime.
Hydrodynamics of the Chiral Dirac Spectrum
Yizhuang Liu; Piotr Warchol; Ismail Zahed
2015-06-29
We derive a hydrodynamical description of the eigenvalues of the chiral Dirac spectrum in the vacuum and in the large $N$ (volume) limit. The linearized hydrodynamics supports sound waves. The stochastic relaxation of the eigenvalues is captured by a hydrodynamical instanton configuration which follows from a pertinent form of Euler equation. The relaxation from a phase of localized eigenvalues and unbroken chiral symmetry to a phase of de-localized eigenvalues and broken chiral symmetry occurs over a time set by the speed of sound. We show that the time is $\\Delta \\tau=\\pi\\rho(0)/2\\beta N$ with $\\rho(0)$ the spectral density at zero virtuality and $\\beta=1,2,4$ for the three Dyson ensembles that characterize QCD with different quark representations in the ergodic regime.
Local characteristic algorithms for relativistic hydrodynamics
Jose A. Font
2002-03-22
Numerical schemes for the general relativistic hydrodynamic equations are discussed. The use of conservative algorithms based upon the characteristic structure of those equations, developed during the last decade building on ideas first applied in Newtonian hydrodynamics, provides a robust methodology to obtain stable and accurate solutions even in the presence of discontinuities. The knowledge of the wave structure of the above system is essential in the construction of the so-called linearized Riemann solvers, a class of numerical schemes specifically designed to solve nonlinear hyperbolic systems of conservation laws. In the last part of the review some astrophysical applications of such schemes, using the coupled system of the (characteristic) Einstein and hydrodynamic equations, are also briefly presented.
Analysis of Galaxy Formation with Hydrodynamics
P. B. Tissera; D. G. Lambas; M. G. Abadi
1996-03-28
We present a hydrodynamical code based on the Smooth Particle Hydrodynamics technique implemented in an AP3M code aimed at solving the hydrodynamical and gravitational equations in a cosmological frame. We analyze the ability of the code to reproduce standard tests and perform numerical simulations to study the formation of galaxies in a typical region of a CDM model. These numerical simulations include gas and dark matter particles and take into account physical processes such as shock waves, radiative cooling, and a simplified model of star formation. Several observed properties of normal galaxies such as $M_{gas}/M_{total}$ ratios, the luminosity function and the Tully-Fisher relation are analyzed within the limits imposed by numerical resolution.
The application of sodium amalgam to prepare ferrofluids containing iron particles in mercury
NASA Astrophysics Data System (ADS)
Takács, L.
1988-04-01
Mercury-based ferrofluids are prepared by using sodium amalgam to reduce iron into mercury while agitating mechanically and magnetically by an ordinary magnetic stirrer. The field dependence of the room-temperature magnetization is measured and used to determine the particle size distribution and its aging behavior. Samples prepared by the conventional method of electroplating into a mercury cathode are also studied for comparison. It is shown that the samples prepared by the two methods are very similar and the small amount of sodium remaining in the samples prepared from sodium amalgam can enhance the stability.
NASA Astrophysics Data System (ADS)
Joshi, Tilak; Singh, Shri; Choudhary, Amit; Pant, R. P.; Biradar, A. M.
2013-07-01
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.
Local Radiative Hydrodynamic and Magnetohydrodynamic Instabilities in Optically Thick Media
Omer Blaes; Aristotle Socrates
2003-01-01
We examine the local conditions for radiative damping and driving of short-wavelength, propagating hydrodynamic and magnetohydrodynamic (MHD) waves in static, optically thick, stratified equilibria. We show that so-called strange modes in stellar oscillation theory and magnetic photon bubbles are intimately related and are both fundamentally driven by the background radiation flux acting on compressible waves. We identify the necessary criteria
Zhu, Taotao; Cheng, Rui; Sheppard, Gareth R; Locklin, Jason; Mao, Leidong
2015-08-11
We report a novel magnetic-field-assisted method for the fabrication and manipulation of nonspherical polymer particles within a ferrofluid-based droplet microfluidic device. Shape control and chain assembly of droplets with tunable lengths have been achieved. PMID:26212067
Torres-Diaz, I.; Cortes, A.; Rinaldi, C., E-mail: carlos.rinaldi@bme.ufl.edu [Department of Chemical Engineering, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9000 (United States); Cedeño-Mattei, Y. [Department of Chemistry, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9019 (United States)] [Department of Chemistry, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9019 (United States); Perales-Perez, O. [Department of Engineering Science and Materials, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9044 (United States)] [Department of Engineering Science and Materials, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9044 (United States)
2014-01-15
Ferrofluid flow in cylindrical and annular geometries under the influence of a uniform rotating magnetic field was studied experimentally using aqueous ferrofluids consisting of low concentrations (<0.01 v/v) of cobalt ferrite nanoparticles with Brownian relaxation to test the ferrohydrodynamic equations, elucidate the existence of couple stresses, and determine the value of the spin viscosity in these fluids. An ultrasound technique was used to measure bulk velocity profiles in the spin-up (cylindrical) and annular geometries, varying the intensity and frequency of the rotating magnetic field generated by a two pole stator winding. Additionally, torque measurements in the cylindrical geometry were made. Results show rigid-body like velocity profiles in the bulk, and no dependence on the axial direction. Experimental velocity profiles were in quantitative agreement with the predictions of the spin diffusion theory, with a value of the spin viscosity of ?10{sup ?8} kg m/s, two orders of magnitude larger than the value estimated earlier for iron oxide based ferrofluids, and 12 orders of magnitude larger than estimated using dimensional arguments valid in the infinite dilution limit. These results provide further evidence of the existence of couple stresses in ferrofluids and their role in driving the spin-up flow phenomenon.
Hydrodynamics of vegetated channels
Nepf, Heidi
This paper highlights some recent trends in vegetation hydrodynamics, focusing on conditions within channels and spanning spatial scales from individual blades, to canopies or vegetation patches, to the channel reach. At ...
Sun, Yi; Kwok, Yien-Chian; Foo-Peng Lee, Peter; Nguyen, Nam-Trung
2009-07-01
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
Spreading of a ferrofluid core in three-stream micromixer channels
NASA Astrophysics Data System (ADS)
Wang, Zhaomeng; Varma, V. B.; Xia, Huan Ming; Wang, Z. P.; Ramanujan, R. V.
2015-05-01
Spreading of a water based ferrofluid core, cladded by a diamagnetic fluid, in three-stream micromixer channels was studied. This spreading, induced by an external magnetic field, is known as magnetofluidic spreading (MFS). MFS is useful for various novel applications where control of fluid-fluid interface is desired, such as micromixers or micro-chemical reactors. However, fundamental aspects of MFS are still unclear, and a model without correction factors is lacking. Hence, in this work, both experimental and numerical analyses were undertaken to study MFS. We show that MFS increased for higher applied magnetic fields, slower flow speed of both fluids, smaller flow rate of ferrofluid relative to cladding, and higher initial magnetic particle concentration. Spreading, mainly due to connective diffusion, was observed mostly near the channel walls. Our multi-physics model, which combines magnetic and fluidic analyses, showed, for the first time, excellent agreement between theory and experiment. These results can be useful for lab-on-a-chip devices.
Hoff, Dan; Sheikh, Lubna; Bhattacharya, Soumya; Nayar, Suprabha; Webster, Thomas J
2013-01-01
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
NASA Astrophysics Data System (ADS)
Nekhoroshkova, Yu. E.; Goldina, O. A.; Camp, P. J.; Elfimova, E. A.; Ivanov, A. O.
2014-03-01
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.
Protein-polymer functionalized aqueous ferrofluids showing high T2 relaxivity.
Bhattacharya, S; Sheikh, L; Tiwari, V; Ghosh, M; Patel, J N; Patel, A B; Nayar, S
2014-05-01
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
Ferrofluid based dispersive-solid phase extraction for spectrophotometric determination of dyes.
Davudabadi Farahani, Malihe; Shemirani, Farzaneh
2013-10-01
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
NASA Astrophysics Data System (ADS)
Rablau, Corneliu; Vaishnava, Prem; Sudakar, Chandran; Tackett, Ronald; Lawes, Gavin; Naik, Ratna
2008-08-01
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.
Takahashi, Hayato; Nagao, Daisuke; Watanabe, Kanako; Ishii, Haruyuki; Konno, Mikio
2015-05-26
Monodisperse, nonmagnetic, asymmetrical composite dumbbells in a suspension of magnetic nanoparticles (ferrofluid) were aligned by application of an external magnetic field to the ferrofluid. The asymmetrical composite dumbbells were prepared by two-step soap-free emulsion polymerization consisting of the first polymerization to coat spherical silica cores with cross-linked poly(methyl methacrylate) (PMMA) shell and the second polymerization to protrude a polystyrene (PSt) lobe from the core-shell particles. A chain structure of nonmagnetic dumbbells oriented to the applied magnetic field was observed at nanoparticle content of 2.0 vol % and field strengths higher than 1.0 mT. A similar chain structure of the dumbbells was observed under application of alternating electric field at strengths higher than 50 V/mm. Parallel and orthogonally combined applications of the electric and magnetic fields were also conducted to examine independence of the electric and magnetic applications as operational factors in the dumbbell assembling. Dumbbell chains stiffer than those in a single application of external field were formed in the parallel combined application of electric and magnetic fields. The orthogonal combination of the different applied fields could form a magnetically aligned chain structure of the nonmagnetic dumbbells oriented to the electric field. The present work experimentally indicated that the employment of inverse magnetorheological effect for nonmagnetic, anisotropic particles can be a useful method for the simultaneous controls over the orientation and the positon of anisotropic particles in their assembling. PMID:25927488
A ferrofluid-based neural network: design of an analogue associative memory
NASA Astrophysics Data System (ADS)
Palm, R.; Korenivski, V.
2009-02-01
We analyse an associative memory based on a ferrofluid, consisting of a system of magnetic nano-particles suspended in a carrier fluid of variable viscosity subject to patterns of magnetic fields from an array of input and output magnetic pads. The association relies on forming patterns in the ferrofluid during a training phase, in which the magnetic dipoles are free to move and rotate to minimize the total energy of the system. Once equilibrated in energy for a given input- output magnetic field pattern pair, the particles are fully or partially immobilized by cooling the carrier liquid. Thus produced particle distributions control the memory states, which are read out magnetically using spin-valve sensors incorporated into the output pads. The actual memory consists of spin distributions that are dynamic in nature, realized only in response to the input patterns that the system has been trained for. Two training algorithms for storing multiple patterns are investigated. Using Monte Carlo simulations of the physical system, we demonstrate that the device is capable of storing and recalling two sets of images, each with an accuracy approaching 100%.
The effect of particle interactions on Curie-Weiss behavior in ferrofluids
NASA Astrophysics Data System (ADS)
Popplewell, J.; Abu Aisheh, B.; Ayoub, N. Y.
1988-11-01
The initial susceptibility of a number of Fe3 O4 particle ferrofluids with volume concentrations, ?=0.08, 0.07, 0.05, 0.03, 0.02, and 0.01 (prepared by diluting a stock fluid of Ms =40 kA m-1) has been measured in the temperature range 220-450 K. The mean particle sizes Dm (magnetic) and Dp (physical) are 74 and 81 Å, respectively. The ferrofluids exhibit Curie-Weiss-type behavior with negative (Néel) temperature temperature intercepts To . The form of the Curie-Weiss behavior is interpreted as arising from particle interactions which are strong enough to reduce the initial susceptibility below the noninteracting value in the temperature range of measurements. It is suggested that interactions lead to the formation of closed particle structures of zero moment in zero field and, as would be the case for an antiferromagnetic material, leads to Curie-Weiss behavior with a negative ``Néel'' temperature. Negative values of To are thus characteristic of an interacting particle system.
NASA Astrophysics Data System (ADS)
Zeng, Jian
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
Hydrodynamic Instability and Coalescence of Binary Neutron Stars
Dong Lai; Frederic A. Rasio; Stuart L. Shapiro
1993-01-01
We study the importance of hydrodynamic effects on the evolution of\\u000acoalescing binary neutron stars. Using an approximate energy functional\\u000aconstructed from equilibrium solutions for polytropic binary configurations, we\\u000aincorporate hydrodynamic effects into the calculation of the orbital decay\\u000adriven by gravitational wave emission. In particular, we follow the transition\\u000abetween the quasi-static, secular decay of the orbit at large
Test problems for radiation and radiation-hydrodynamics codes
NASA Technical Reports Server (NTRS)
Ensman, Lisa
1994-01-01
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.
Klein-Gordon Equation in Hydrodynamical Form
Wong, Cheuk-Yin [ORNL
2010-01-01
We follow and modify the Feshbach-Villars formalism by separating the Klein-Gordon equation into two coupled time-dependent Schroedinger equations for the particle and antiparticle wave functions with positive probability densities. We find that the equation of motion for the probability densities is in the form of relativistic hydrodynamics where various forces have their physical and classical counterparts. An additional element is the presence of the quantum stress tensor that depends on the derivatives of the amplitude of the wave function.
Hydrodynamics with Triangle Anomalies
Son, Dam T
2009-01-01
We consider the hydrodynamic regime of theories with quantum anomalies for global currents. We show that a hitherto discarded term in the conserve current is not only allowed by symmetries, but is in fact required by triangle anomalies and the second law of thermodynamics. This term leads to a number of new effects, one of which is chiral separation in a rotating fluid at nonzero chemical potential. The new kinetic coefficients can be expressed, in a unique fashion, through the anomalies coefficients and the equation of state. We briefly discuss the relevance of this new hydrodynamic term for physical situations, including heavy ion collisions.
Hydrodynamics with Triangle Anomalies
Son, Dam T.; Surowka, Piotr
2009-11-06
We consider the hydrodynamic regime of theories with quantum anomalies for global currents. We show that a hitherto discarded term in the conserved current is not only allowed by symmetries, but is in fact required by triangle anomalies and the second law of thermodynamics. This term leads to a number of new effects, one of which is chiral separation in a rotating fluid at nonzero chemical potential. The new kinetic coefficients can be expressed, in a unique fashion, through the anomaly coefficients and the equation of state. We briefly discuss the relevance of this new hydrodynamic term for physical situations, including heavy-ion collisions.
Purely hydrodynamic origin for swarming of swimming particles
Norihiro Oyama; John Jairo Molina; Ryoichi Yamamoto
2015-09-29
Three-dimensional simulations with fully resolved hydrodynamics are performed to study the collective motion of model swimmers in confinement. We show that certain swimming mechanisms can lead to traveling wave-like collective motion even without any direct alignment mechanism. It is also shown that by varying the swimming mechanism, this collective motion can be suppressed, contrary to the perception that hydrodynamic effects are completely screened at high volume fraction. From an analysis of bulk systems, it is shown that this traveling wave-like motion, which can be characterized as a pseudo-acoustic mode, is mainly due to the intrinsic swimming property of the particles.
Investigation of temperature dependent magnetic hyperthermia in Fe3O4 ferrofluids
NASA Astrophysics Data System (ADS)
Nemala, Humeshkar Bhaskar
Magnetic nanoparticles (MNPs) of Fe3O4 and gamma-Fe2O3 have been exploited in the biomedical fields for imaging, targeted drug delivery and magnetic hyperthermia. Magnetic hyperthermia (MHT), the production of heat using ferrofluids, colloidal suspensions of MNPs, in an external AC magnetic field (amplitude, 100-500 Oe and frequency 50 kHz -1MHz), has been explored by many researchers, both in vitro and in vivo, as an alternative viable option to treat cancer. The heat energy generated by Neel and Brownian relaxation processes of the internal magnetic spins could be used to elevate local tissue temperature to about 46 ?C to arrest cancerous growth. MHT, due to its local nature of heating, when combined with other forms of treatment such as chemotherapy and/or radiation therapy, it could become an effective therapy for cancer treatment. The efficiency of heat production in MHT is quantified by specific absorption rate (SAR), defined as the power output per gram of the MNPs used. In this thesis, ferrofluids consisting of Fe3O4 MNPs of three different sizes (˜ 10 - 13 nm) coated with two different biocompatible surfactants, dextran and polyethylene glycol (PEG), have been investigated. The structural and magnetic characterization of the MNPs were done using XRD, TEM, and DC magnetization measurements. While XRD revealed the crystallite size, TEM provided the information about morphology and physical size distribution of the MNPs. Magnetic measurements of M-vs-H curves for ferrofluids provided information about the saturation magnetization (Ms) and magnetic core size distribution of MNPs. Using MHT measurements, the SAR has been studied as a function of temperature, taking into account the heat loss due to non-adiabatic nature of the experimental set-up. The observed SAR values have been interpreted using the theoretical framework of linear response theory (LRT). We found the SAR values depend on particle size distribution of MNPs, Ms (65-80 emu/g) and the magnetic anisotropy energy density (K: 12-20 KJ/m3), as well as the amplitude and frequency of the applied AC field (amplitude, 150-250 Oe and frequency, 180-380 kHz). In general, Ms and magnetic core diameter of MNPs increased with the increase in particle size. However, our detailed analysis of MHT data show that although SAR increased with the particle size, the polydispersity of the particles as well as the magnetic anisotropy energy density significantly affected the SAR values. Dextran and PEG coatings essentially yielded similar SAR values ~ 100 W/g using ferrofluids of Fe3O4 MNPs with an average crystallite size of 11.6 +/- 2.1 nm, in AC field of 245 Oe and 375 KHz.
Deng, Ming; Huang, Can; Liu, Danhui; Jin, Wei; Zhu, Tao
2015-08-10
An ultra-compact optical fiber magnetic field sensor based on a microstructured optical fiber (MOF) modal interference and ferrofluid (FF) has been proposed and experimentally demonstrated. The magnetic field sensor was fabricated by splicing a tapered germanium-doped index guided MOF with six big holes injected with FF to two conventional single-mode fibers. The transmission spectra of the proposed sensor under different magnetic field intensities have been measured and theoretically analyzed. Due to an efficient interaction between the magnetic nanoparticles in FF and the excited cladding mode, the magnetic field sensitivity reaches up to117.9pm/mT with a linear range from 0mT to 30mT. Moreover, the fabrication process of the proposed sensor is simple, easy and cost-effective. Therefore, it will be a promising candidate for military, aviation industry, and biomedical applications, especially, for the applications where the space is limited. PMID:26367919
Linke, J M; Odenbach, S
2015-05-01
The anisotropy of the magnetoviscous effect of a ferrofluid has been studied in a specially designed slit die viscometer, which allows three distinct orientations of the magnetic field with respect to the fluid flow. The corresponding Miesowicz viscosity coefficients were determined in dependence of the shear rate and the magnetic field intensity to gain a comprehensive magnetorheological characterization of the fluid. The particles in the fluid have a mean diameter of 13 nm corresponding to an interaction parameter of ? ? 1.3 for magnetite. Thus, the fluid can be expected to show a transition from non-interacting individual particles to microstructures with chain-like associated particles when the magnetic field intensity is increased and the shear rate is decreased. The observed field and shear dependent anisotropy of the magnetoviscous effect is explained coherently in terms of these microstructural changes in the fluid. PMID:25837303
Stochastic dynamics of superparamagnetic moments in polidisperse ferrofluids
NASA Astrophysics Data System (ADS)
Scherer, C.
2007-12-01
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.
COCHLEAR HYDRODYNAMICS DEMYSTIFIED
Allen, Jont
45], and of J. W. S. Rayleigh, The Theory of Sound [Rayleigh 45], which explain fluid flow problems, as is Rayleigh's section on capillarity. Our treatment of the hydrodynamics is rather lengthy, due to our attempt]. The effect of the outer hair cells is included as a variable negative damping term; the variable damping
Disorders of CSF hydrodynamics.
Johnston, I; Teo, C
2000-11-01
This article reviews the range of hydrodynamic disorders affecting the CSF circulation. Initially consideration is given to questions of definition and classification. A scheme for the practical, clinical analysis for the diagnosis of such disorders is then presented. The physiology and pathophysiology of the CSF circulation is reviewed, with particular emphasis on issues that remain unresolved. This provides a background to consideration of the adverse consequences of abnormal CSF hydrodynamics, again focusing on areas where further information is required. Methods of clinical investigation of CSF hydrodynamics are reviewed, followed by general considerations of treatment. Finally, each of the main, clinically important, forms of disordered CSF hydrodynamics is briefly considered, with particular emphasis, again, on areas where current knowledge is deficient. The conditions considered include hydrocephalus of various forms (childhood, adult, arrested, multi-compartment), infantile macrocephaly, arachnoid and glioependymal cysts, syringo- and hydromyelia, pseudotumour cerebri, impaired cranial venous outflow, altered CSF composition, shunt obstruction without ventricular enlargement and low-CSF-pressure states. PMID:11151732
Skew resisting hydrodynamic seal
Conroy, William T. (Pearland, TX); Dietle, Lannie L. (Sugar Land, TX); Gobeli, Jeffrey D. (Houston, TX); Kalsi, Manmohan S. (Houston, TX)
2001-01-01
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.
Allen M. Teeter; Billy H. Johnson; Charlie Berger; Guus Stelling; Norman W. Scheffner; Marcelo H. Garcia; T. M. Parchure
2001-01-01
Modeling capabilities for shallow, vegetated, systems are reviewed to assess hydrodynamic, wind and wave, submersed plant friction, and sediment transport aspects. Typically, ecosystems with submersed aquatic vegetation are relatively shallow, physically stable and of moderate hydrodynamic energy. Wind-waves are often important to sediment resuspension. These are open systems that receive flows of material and energy to various degrees around their
Synthesis and characterization of iron-rich FexPt1-x ferrofluid for magnetic resonance imaging
NASA Astrophysics Data System (ADS)
Jha, Deepak K.; Deb, P.; Kalita, E.; Shameem, M.; Patel, Anant B.
2012-03-01
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.
Hyperbolic metamaterial lens with hydrodynamic nonlocal response.
Yan, Wei; Mortensen, N Asger; Wubs, Martijn
2013-06-17
We investigate the effects of hydrodynamic nonlocal response in hyperbolic metamaterials (HMMs), focusing on the experimentally realizable parameter regime where unit cells are much smaller than an optical wavelength but much larger than the wavelengths of the longitudinal pressure waves of the free-electron plasma in the metal constituents. We derive the nonlocal corrections to the effective material parameters analytically, and illustrate the noticeable nonlocal effects on the dispersion curves numerically. As an application, we find that the focusing characteristics of a HMM lens in the local-response approximation and in the hydrodynamic Drude model can differ considerably. In particular, the optimal frequency for imaging in the nonlocal theory is blueshifted with respect to that in the local theory. Thus, to detect whether nonlocal response is at work in a hyperbolic metamaterial, we propose to measure the near-field distribution of a hyperbolic metamaterial lens. PMID:23787690
Hydrodynamic modeling of tsunamis from the Currituck landslide Eric L. Geist a,
Lynett, Patrick
Hydrodynamic modeling of tsunamis from the Currituck landslide Eric L. Geist a, , Patrick J. Lynett: Accepted 24 September 2008 Keywords: tsunami landslide hydrodynamic runup numerical model sensitivity analysis Tsunami generation from the Currituck landslide offshore North Carolina and propagation of waves
Active Carbon and Oxygen Shell Burning Hydrodynamics Casey A. Meakin1
Arnett, W. David
Active Carbon and Oxygen Shell Burning Hydrodynamics Casey A. Meakin1 & David Arnett1 cmeakin occur between active carbon and oxygen burning shells, (2) hydrodynamic wave motions in nonconvective. A Double Shell Model: Active Oxygen and Carbon Burning Previously we have evolved a 23M model with the one
Modeling of textural changes in beef loins subjected to hydrodynamic pressure
Technology Transfer Automated Retrieval System (TEKTRAN)
High hydrodynamic pressure has been considered as a new novel food processing technique to impart favorable textural changes in meat. It is believed that a hydrodynamic pressure wave could be used to tenderize otherwise unacceptably tough cuts of beef, and allow them to be used in more valuable prod...
On some properties of kinetic and hydrodynamic equations for inelastic interactions
On some properties of kinetic and hydrodynamic equations for inelastic interactions A. V. Bobylev equation. We obtain formally a hydrodynamic description for near elastic particles under the assumption of constant and variable restitution coeffi cient. We describe the linear longwave stability/instability
Nonlinear hydrodynamics. Lecture 9
Cox, A.N.
1983-03-14
A very sophisticated method for calculating the stability and pulsations of stars which make contact with actual observations of the stellar behavior, hydrodynamic calculations are very simple in principle. Conservation of mass can be accounted for by having mass shells that are fixed with their mass for all time. Motions of these shells can be calculated by taking the difference between the external force of gravity and that from the local pressure gradient. The conservation of energy can be coupled to this momentum conservation equation to give the current temperatures, densities, pressures, and opacities at the shell centers, as well as the positions, velocities, and accelerations of the mass shell interfaces. Energy flow across these interfaces can be calculated from the current conditions, and this energy is partitioned between internal energy and the work done on or by the mass shell. We discuss here only the purely radial case for hydrodynamics because it is very useful for stellar pulsation studies.
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.
Relativistic cosmological hydrodynamics
J. Hwang; H. Noh
1997-11-29
We investigate the relativistic cosmological hydrodynamic perturbations. We present the general large scale solutions of the perturbation variables valid for the general sign of three space curvature, the cosmological constant, and generally evolving background equation of state. The large scale evolution is characterized by a conserved gauge invariant quantity which is the same as a perturbed potential (or three-space curvature) in the comoving gauge.
A. Sudarshan; S. K. Sharma
1992-01-01
In this paper we study the stimulated scattering of an electromagnetic wave by an ion-cyclotron wave perturbation in a two electron temperature plasma. The hydrodynamic equations have been used to derive the dispersion relation for the scattered wave following the three wave interaction formalism. Explicit expressions for the growth rate of the scattered wave have been derived. Our results show
Hydrodynamics of fossil fishes.
Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert
2014-08-01
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
Hydrodynamics of fossil fishes
Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert
2014-01-01
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
Building a Hydrodynamics Code with Kinetic Theory
NASA Astrophysics Data System (ADS)
Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Pickett, Rodney; Strother, Terrance
2013-08-01
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.
Inactivation and injury of pathogenic bacteria by hydrodynamic pressure treatment
Technology Transfer Automated Retrieval System (TEKTRAN)
Hydrodynamic pressure processing (HDP) is an innovative non-thermal technology developed for improving meat tenderness. The shock waves generated in the HDP process cause significant disruption of myofibrillar proteins in muscle tissue resulting in improved tenderness of various beef cuts. The same ...
Hydrodynamic instabilities in supernova remnants: Early radiative cooling
Roger Chevalier; John M. Blondin
1995-01-01
The initial interaction of a supernova with its surrounding medium gives rise to a double shell structure bounded by shock waves, in which the deceleration of the supernova gas is subject to hydrodynamic instabilities. For the case where the surrounding medium is a circumstellar wind, the high density at early times can give rise to radiative cooling of the shocked
A new shock-capturing numerical scheme for ideal hydrodynamics
NASA Astrophysics Data System (ADS)
Fecková, Z.; Tomášik, B.
2015-05-01
We present a new algorithm for solving ideal relativistic hydrodynamics based on Godunov method with an exact solution of Riemann problem for an arbitrary equation of state. Standard numerical tests are executed, such as the sound wave propagation and the shock tube problem. Low numerical viscosity and high precision are attained with proper discretization.
A new shock-capturing numerical scheme for ideal hydrodynamics
Feckova, Zuzana
2015-01-01
We present a new algorithm for solving ideal relativistic hydrodynamics based on Godunov method with an exact solution of Riemann problem for an arbitrary equation of state. Standard numerical tests are executed, such as the sound wave propagation and the shock tube problem. Low numerical viscosity and high precision are attained with proper discretization.
A new shock-capturing numerical scheme for ideal hydrodynamics
Zuzana Feckova; Boris Tomasik
2015-01-07
We present a new algorithm for solving ideal relativistic hydrodynamics based on Godunov method with an exact solution of Riemann problem for an arbitrary equation of state. Standard numerical tests are executed, such as the sound wave propagation and the shock tube problem. Low numerical viscosity and high precision are attained with proper discretization.
Naoki Yamamoto
2015-05-20
We study the hydrodynamic regime of chiral plasmas at high temperature. We find a new type of gapless collective excitation induced by chiral effects in an external magnetic field. This is a transverse wave and is present even in incompressible fluids, unlike the chiral magnetic and chiral vortical waves. The velocity is proportional to the coefficient of the gravitational anomaly. We briefly discuss possible relevance of this "chiral Alfv\\'en wave" in physical systems.
NASA Technical Reports Server (NTRS)
Sabelman, E. E. (inventor)
1973-01-01
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.
Hydrodynamic phase-locking of swimming microorganisms
Gwynn J. Elfring; Eric Lauga
2009-07-06
Some microorganisms, such as spermatozoa, synchronize their flagella when swimming in close proximity. Using a simplified model (two infinite, parallel, two-dimensional waving sheets), we show that phase-locking arises from hydrodynamics forces alone, and has its origin in the front-back asymmetry of the geometry of their flagellar waveform. The time-evolution of the phase difference between co-swimming cells depends only on the nature of this geometrical asymmetry, and microorganisms can phase-lock into conformations which minimize or maximize energy dissipation.
Hydrodynamic Phase Locking of Swimming Microorganisms
NASA Astrophysics Data System (ADS)
Elfring, Gwynn J.; Lauga, Eric
2009-08-01
Some microorganisms, such as spermatozoa, synchronize their flagella when swimming in close proximity. Using a simplified model (two infinite, parallel, two-dimensional waving sheets), we show that phase locking arises from hydrodynamics forces alone, and has its origin in the front-back asymmetry of the geometry of their flagellar waveform. The time evolution of the phase difference between coswimming cells depends only on the nature of this geometrical asymmetry, and microorganisms can phase lock into conformations which minimize or maximize energy dissipation.
Fast Lattice Boltzmann Solver for Relativistic Hydrodynamics
NASA Astrophysics Data System (ADS)
Mendoza, M.; Boghosian, B. M.; Herrmann, H. J.; Succi, S.
2010-07-01
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.
Postexplosion hydrodynamics of supernovae in red supergiants
NASA Technical Reports Server (NTRS)
Herant, Marc; Woosley, S. E.
1994-01-01
Shock propagation, mixing, and clumping are studied in the explosion of red supergiants as Type II supernovae using a two-dimensional smooth particle hydrodynamic (SPH) code. We show that extensive Rayleigh-Talor instabilities develop in the ejecta in the wake of the reverse shock wave. In all cases, the shell structure of the progenitor is obliterated to leave a clumpy, well-mixed supernova remnant. However, the occurrence of mass loss during the lifetime of the progenitor can significantly reduce the amount of mixing. These results are independent of the Type II supernova explosion mechanism.
Evaluation of using ferrofluid as an interface material for a field-reversible thermal connector
NASA Astrophysics Data System (ADS)
Yousif, Ahmed S.
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.
Sprenger, Lisa Lange, Adrian; Odenbach, Stefan
2014-02-15
Ferrofluids consist of magnetic nanoparticles dispersed in a carrier liquid. Their strong thermodiffusive behaviour, characterised by the Soret coefficient, coupled with the dependency of the fluid's parameters on magnetic fields is dealt with in this work. It is known from former experimental investigations on the one hand that the Soret coefficient itself is magnetic field dependent and on the other hand that the accuracy of the coefficient's experimental determination highly depends on the volume concentration of the fluid. The thermally driven separation of particles and carrier liquid is carried out with a concentrated ferrofluid (? = 0.087) in a horizontal thermodiffusion cell and is compared to equally detected former measurement data. The temperature gradient (1 K/mm) is applied perpendicular to the separation layer. The magnetic field is either applied parallel or perpendicular to the temperature difference. For three different magnetic field strengths (40 kA/m, 100 kA/m, 320 kA/m) the diffusive separation is detected. It reveals a sign change of the Soret coefficient with rising field strength for both field directions which stands for a change in the direction of motion of the particles. This behaviour contradicts former experimental results with a dilute magnetic fluid, in which a change in the coefficient's sign could only be detected for the parallel setup. An anisotropic behaviour in the current data is measured referring to the intensity of the separation being more intense in the perpendicular position of the magnetic field: S{sub T?} = ?0.152 K{sup ?1} and S{sub T?} = ?0.257 K{sup ?1} at H = 320 kA/m. The ferrofluiddynamics-theory (FFD-theory) describes the thermodiffusive processes thermodynamically and a numerical simulation of the fluid's separation depending on the two transport parameters ?{sub ?} and ?{sub ?} used within the FFD-theory can be implemented. In the case of a parallel aligned magnetic field, the parameter can be determined to ?{sub ?} = (2.8;?9.1;?11.2)?×?10{sup ?11}?·?D{sub ?} kg/(A{sup 2}m) for the different field strengths and in dependence on the magnetic diffusion coefficient D{sub ?}. An adequate fit in the perpendicular case is not possible, by ?{sub ?} = 1?×?10{sup ?17} kg/(Am{sup 2}) a rather good agreement between numerical and experimental data can be found for a field strength of 40 kA/m, a change in the coefficient's sign in the perpendicular setup is not numerically determinable via this theory. The FFD-theory is only partly applicable to calculate the concentration profile in concentrated magnetic fluids established due to a temperature gradient and magnetic field applied.
EUNHA: a New Cosmological Hydrodynamic Simulation Code
NASA Astrophysics Data System (ADS)
Shin, Jihye; Kim, Juhan; Kim, Sungsoo S.; Park, Changbom
2014-06-01
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.
Anisotropic Flow and Viscous Hydrodynamics
Li Yan
2012-08-15
We report part of our recent work on viscous hydrodynamics with consistent phase space distribution $f(x,\\p)$ for freeze out. We develop the gradient expansion formalism based on kinetic theory, and with the constraints from the comparison between hydrodynamics and kinetic theory, viscous corrections to $f(x,\\p)$ can be consistently determined order by order. Then with the obtained $f(x,\\p)$, second order viscous hydrodynamical calculations are carried out for elliptic flow $v_2$.
Incompressible smoothed particle hydrodynamics
Ellero, Marco Serrano, Mar; Espanol, Pep
2007-10-01
We present a smoothed particle hydrodynamic model for incompressible fluids. As opposed to solving a pressure Poisson equation in order to get a divergence-free velocity field, here incompressibility is achieved by requiring as a kinematic constraint that the volume of the fluid particles is constant. We use Lagrangian multipliers to enforce this restriction. These Lagrange multipliers play the role of non-thermodynamic pressures whose actual values are fixed through the kinematic restriction. We use the SHAKE methodology familiar in constrained molecular dynamics as an efficient method for finding the non-thermodynamic pressure satisfying the constraints. The model is tested for several flow configurations.
NASA Astrophysics Data System (ADS)
Voskresensky, D. N.
2011-01-01
We derive system of equations describing fluidity of the medium consisting of non-relativistic particles with finite mass-widths. For that we use expressions for the kinetic Noether 4-current and the Noether energy-momentum tensor being conserved provided one uses self-consistent approximations to the gradient expanded Kadanoff-Baym equations. Kinetic coefficients entering equations of non-ideal hydrodynamics of resonances are obtained in terms of the real and imaginary parts of the self-energies within a relaxation time approximation.
Lifshitz superfluid hydrodynamics
NASA Astrophysics Data System (ADS)
Chapman, Shira; Hoyos, Carlos; Oz, Yaron
2014-07-01
We construct the first order hydrodynamics of quantum critical points with Lifshitz scaling and a spontaneously broken symmetry. The fluid is described by a combination of two flows, a normal component that carries entropy and a super-flow which has zero viscosity and carries no entropy. We analyze the new transport effects allowed by the lack of boost invariance and constrain them by the local second law of thermodynamics. Imposing time-reversal invariance, we find eight new parity even transport coefficients. The formulation is applicable, in general, to any superfluid/superconductor with an explicit breaking of boost symmetry, in particular to high T c superconductors. We discuss possible experimental signatures.
Hydrodynamic interactions in colloidal crystals
Weeber, Rudolf
2011-01-01
In dense colloids it is commonly assumed that hydrodynamic interactions do not play a role. However, a found theoretical quantification is often missing. We present computer simulations that are motivated by experiments where a large colloidal particle is dragged through a colloidal crystal. To qualify the influence of long-ranged hydrodynamics, we model the setup by conventional Langevin dynamics simulations and by an improved scheme with limited hydrodynamic interactions. This scheme significantly improves our results and allows to show that hydrodynamics strongly impacts on the development of defects, the crystal regeneration as well as on the jamming behavior.
The Quantum Hydrodynamic Description of Tunneling
Kendrick, Brian K. [Los Alamos National Laboratory
2012-06-15
The quantum hydrodynamic approach is based on the de Broglie-Bohm formulation of quantum mechanics. The resulting fluid-like equations of motion describe the flow of probability and an accurate solution to these equations is equivalent to solving the time-dependent Schroedinger equation. Furthermore, the hydrodynamic approach provides new insight into the mechanisms as well as an alternative computational approach for treating tunneling phenomena. New concepts include well-defined 'quantum trajectories', 'quantum potential', and 'quantum force' all of which have classical analogues. The quantum potential and its associated force give rise to all quantum mechanical effects such as zero point energy, tunneling, and interference. A new numerical approach called the Iterative Finite Difference Method (IFDM) will be discussed. The IFDM is used to solve the set of non-linear coupled hydrodynamic equations. It is 2nd-order accurate in both space and time and exhibits exponential convergence with respect to the iteration count. The stability and computational efficiency of the IFDM is significantly improved by using a 'smart' Eulerian grid which has the same computational advantages as a Lagrangian or Arbitrary Lagrangian Eulerian (ALE) grid. The IFDM is also capable of treating anharmonic potentials. Example calculations using the IFDM will be presented which include: a one-dimensional Gaussian wave packet tunneling through an Eckart barrier, a one-dimensional bound-state Morse oscillator, and a two-dimensional (2D) model collinear reaction using an anharmonic potential energy surface. Approximate treatments of the quantum hydrodynamic equations will also be discussed which could allow scaling of the calculations to hundreds of degrees of freedom which is important for treating tunneling phenomena in condensed phase systems.
Klein-Gordon Equation in Hydrodynamical Form
Cheuk-Yin Wong
2010-12-22
We follow and modify the Feshbach-Villars formalism by separating the Klein-Gordon equation into two coupled time-dependent Schroedinger equations for particle and antiparticle wave function components with positive probability densities. We find that the equation of motion for the probability densities is in the form of relativistic hydrodynamics where various forces have their classical counterparts, with the additional element of the quantum stress tensor that depends on the derivatives of the amplitude of the wave function. We derive the equation of motion for the Wigner function and we find that its approximate classical weak-field limit coincides with the equation of motion for the distribution function in the collisionless kinetic theory.
On one-dimensional models for hydrodynamics
Carlos Escudero
2006-06-14
To date it has not been possible to prove whether or not the three-dimensional incompressible Euler equations develop singular behaviour in finite time. Some possible singular scenarios, as for instance shock-waves, are very important from a physical point of view, since they imply the connection among the macroscopic and the microscopic scale. Therefore, the appearence of this type of singularity or a similar one might be interpreted as a possible explanation of the transition to turbulence. In order to clarify the question, some one-dimensional models for ideal incompressible hydrodynamics have been introduced and analyzed, and it was proven that shock-waves appear in finite time within this type of flow. In this work we question the validity of these models and analyze the physical meaning that the occurrence of a singularity in an incompressible flow, if it happens, may have.
On the hydrodynamics of soap films
NASA Astrophysics Data System (ADS)
Couder, Y.; Chomaz, J. M.; Rabaud, M.
1989-07-01
Several experiments aiming at the exploration of the hydrodynamical properties of soap films are presented. Their interpretation takes into account the very specific equation of state of these films. It is shown that on short time scales each element of the film moves as a whole so that the film can be considered as a two-dimensional fluid with a local density proportional to its thickness. When set horizontally, quasi two-dimensional turbulent flows can be obtained. The film behaves as an incompressible fluid whenever the motions occur at velocities small compared to the velocity of its elastic waves. An estimate of the role of air friction is given. The static quasi equilibrium of a film when set vertical is discussed. Phenomena equivalent to the rise of buoyant bubbles can be obtained. It is shown that lee waves can also be generated confirming that a vertical soap film has the dynamical properties of a two-dimensional density stratified fluid.
NASA Astrophysics Data System (ADS)
Huang, Yan; Li, Decai; Li, Feng; Zhu, Quanshui; Xie, Yu
2015-03-01
Using light transmission experiments and optical microscope observations with a longitudinal gradient magnetic field configuration, the relationship between the behavior of the transmitted light relaxation and the microstructure evolution of ionic ferrofluids in the central region of an axisymmetric field is investigated. Under a low-gradient magnetic field, there are two types of relaxation process. When a field is applied, the transmitted light intensity decreases to a minimum within a time on the order of 101-102 s. It is then gradually restored, approaching its initial value within a time on the order of 102 s. This is type I relaxation, which corresponds to the formation of magnetic columns. After the transmission reaches this value, it either increases or decreases slowly, stabilizing within a time on the order of 103 s, according to the direction of the field gradient. This is a type II relaxation, which results from the shadowing effect, corresponding to the motion of the magnetic columns under the application of a gradient force. Under a magnetic field with a centripetal high-gradient (magnetic materials subjected to a force pointing toward the center of the axisymmetric field), the transmitted light intensity decreases monotonously and more slowly than that under a low-gradient field. Magnetic transport and separation resulted from magnetophoresis under high-gradient fields, changing the formation dynamics of the local columns and influencing the final state of the column system.
On the self-assembly of net-like nanostructures in ferrofluids
NASA Astrophysics Data System (ADS)
Elkady, Ashraf S.; Iskakova, Larisa; Zubarev, Andrey
2015-06-01
Understanding the physical forces that govern nanoparticles self-assembly is central to the ability to engineer super-nanostructures for advanced nanotechnology applications. Magnetic force represents one of such important forces that is responsible for structural transformations and condensation in ferrofluids (FF). In this work, we study internal structural transformations in FF in the absence of external magnetic field by introducing the first direct statistical model that takes into account formation of linear chains, Y-forks and net-like nanostructures. The results show that, in agreement with experiments, when the concentration of the magnetic nanoparticles and their magnetic interaction energy are small enough, majority of the particles are united in individual linear chains. But, when these parameters exceed some threshold magnitude, the main particles population switches to net-like nanostructures. These results highlight the importance of magnetic dipole interactions in the absence of external magnetic field, and their essential role in the bottom-up construction of hierarchical nano-architectures of viable fundamental and practical implications.
The Use of Ferrofluids to Model Materials Processing (MSFC Center Director's Discretionary Fund)
NASA Technical Reports Server (NTRS)
Leslie, F.; Ramachandran, N.
2000-01-01
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.
Rajnak, Michal; Kurimsky, Juraj; Dolnik, Bystrik; Kopcansky, Peter; Tomasovicova, Natalia; Taculescu-Moaca, Elena Alina; Timko, Milan
2014-09-01
An experimental study of magnetic colloidal particles cluster formation induced by an external electric field in a ferrofluid based on transformer oil is presented. Using frequency domain isothermal dielectric spectroscopy, we study the influence of a test cell electrode separation distance on a low-frequency relaxation process. We consider the relaxation process to be associated with an electric double layer polarization taking place on the particle surface. It has been found that the relaxation maximum considerably shifts towards lower frequencies when conducting the measurements in the test cells with greater electrode separation distances. As the electric field intensity was always kept at a constant value, we propose that the particle cluster formation induced by the external ac electric field accounts for that phenomenon. The increase in the relaxation time is in accordance with the Schwarz theory of electric double layer polarization. In addition, we analyze the influence of a static electric field generated by dc bias voltage on a similar shift in the relaxation maximum position. The variation of the dc electric field for the hysteresis measurements purpose provides understanding of the development of the particle clusters and their decay. Following our results, we emphasize the utility of dielectric spectroscopy as a simple, complementary method for detection and study of clusters of colloidal particles induced by external electric field. PMID:25314449
NASA Astrophysics Data System (ADS)
Rajnak, Michal; Kurimsky, Juraj; Dolnik, Bystrik; Kopcansky, Peter; Tomasovicova, Natalia; Taculescu-Moaca, Elena Alina; Timko, Milan
2014-09-01
An experimental study of magnetic colloidal particles cluster formation induced by an external electric field in a ferrofluid based on transformer oil is presented. Using frequency domain isothermal dielectric spectroscopy, we study the influence of a test cell electrode separation distance on a low-frequency relaxation process. We consider the relaxation process to be associated with an electric double layer polarization taking place on the particle surface. It has been found that the relaxation maximum considerably shifts towards lower frequencies when conducting the measurements in the test cells with greater electrode separation distances. As the electric field intensity was always kept at a constant value, we propose that the particle cluster formation induced by the external ac electric field accounts for that phenomenon. The increase in the relaxation time is in accordance with the Schwarz theory of electric double layer polarization. In addition, we analyze the influence of a static electric field generated by dc bias voltage on a similar shift in the relaxation maximum position. The variation of the dc electric field for the hysteresis measurements purpose provides understanding of the development of the particle clusters and their decay. Following our results, we emphasize the utility of dielectric spectroscopy as a simple, complementary method for detection and study of clusters of colloidal particles induced by external electric field.
Ferrofluid pipe flow under the influence of the magnetic field of a cylindrical coil
NASA Astrophysics Data System (ADS)
Papadopoulos, P. K.; Vafeas, P.; Hatzikonstantinou, P. M.
2012-12-01
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.
Load responsive hydrodynamic bearing
Kalsi, Manmohan S. (Houston, TX); Somogyi, Dezso (Sugar Land, TX); Dietle, Lannie L. (Stafford, TX)
2002-01-01
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.
Landau Hydrodynamics Reexamined
Cheuk-Yin Wong
2008-11-06
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[\\sqrt{y_b^2-y^2}], where y_b=\\ln[\\sqrt{s_{NN}}/m_p] is the beam nucleon rapidity, instead of Landau's original distribution, dN/dy(Landau) \\exp[\\sqrt{L^2-y^2}], where L=\\ln[\\sqrt{s_{NN}}/2m_p]. 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[-y^2/2L]. 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.
Lectures on Landau Hydrodynamics
Cheuk-Yin Wong
2008-09-02
Landau hydrodynamics is a plausible description for the evolution of the dense hot matter produced in high-energy heavy-ion collisions. We review the formulation of Landau hydrodynamics to pave the way for its application in high-energy heavy-ion collisions. It is found that Landau's rapidity distribution needs to be modified to provide a better quantitative description. In particular, the rapidity distribution in the center-of-mass system should be more appropriately given as dN/dy \\exp{\\sqrt{y_b^2-y^2}}, where y_b=\\ln{\\sqrt{s_NN}/m_p} is the beam nucleon rapidity, instead of Landau's original result of dN/dy({Landau}) \\exp{\\sqrt{L^2-y^2}} where L=\\ln{\\sqrt{s_NN}/2m_p}. The modified distribution is compared with the Landau distribution and experimental data. It is found that the modified distribution agrees better with experimental $dN/dy$ data than the Landau distribution and it differs only slightly from the Landau Gaussian distribution dN/dy(Landau-Gaussian) \\exp{-y^2/2L}. Past successes of the Gaussian distribution in explaining experimental rapidity data arises, not because it is an approximation of the original Landau distribution, but because it is in fact a close representation of the modified distribution.
Active Carbon and Oxygen Shell Burning Hydrodynamics
Casey Meakin; David Arnett
2006-01-16
We have simulated 2.5$\\times10^3$ s of the late evolution of a $23 \\rm M_\\odot$ star with full hydrodynamic behavior. We present the first simulations of a multiple-shell burning epoch, including the concurrent evolution and interaction of an oxygen and carbon burning shell. In addition, we have evolved a 3D model of the oxygen burning shell to sufficiently long times (300 s) to begin to assess the adequacy of the 2D approximation. We summarize striking new results: (1) strong interactions occur between active carbon and oxygen burning shells, (2) hydrodynamic wave motions in nonconvective regions, generated at the convective-radiative boundaries, are energetically important in both 2D and 3D with important consequences for compositional mixing, and (3) a spectrum of mixed p- and g-modes are unambiguously identified with corresponding adiabatic waves in these computational domains. We find that 2D convective motions are exaggerated relative to 3D because of vortex instability in 3D. We discuss the implications for supernova progenitor evolution and symmetry breaking in core collapse.
Generalized hydrodynamics model for strongly coupled plasmas
NASA Astrophysics Data System (ADS)
Diaw, A.; Murillo, M. S.
2015-07-01
Beginning with the exact equations of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, we obtain the density, momentum, and stress tensor-moment equations. We close the moment equations with two closures, one that guarantees an equilibrium state given by density-functional theory and another that includes collisions in the relaxation of the stress tensor. The introduction of a density functional-theory closure ensures self-consistency in the equation-of-state properties of the plasma (ideal and excess pressure, electric fields, and correlations). The resulting generalized hydrodynamics thus includes all impacts of Coulomb coupling, viscous damping, and the high-frequency (viscoelastic) response. We compare our results with those of several known models, including generalized hydrodynamic theory and models obtained using the Singwi-Tosi-Land-Sjolander approximation and the quasilocalized charge approximation. We find that the viscoelastic response, including both the high-frequency elastic generalization and viscous wave damping, is important for correctly describing ion-acoustic waves. We illustrate this result by considering three very different systems: ultracold plasmas, dusty plasmas, and dense plasmas. The new model is validated by comparing its results with those of the current autocorrelation function obtained from molecular-dynamics simulations of Yukawa plasmas, and the agreement is excellent. Generalizations of this model to mixtures and quantum systems should be straightforward.
Generalized hydrodynamics model for strongly coupled plasmas.
Diaw, A; Murillo, M S
2015-07-01
Beginning with the exact equations of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, we obtain the density, momentum, and stress tensor-moment equations. We close the moment equations with two closures, one that guarantees an equilibrium state given by density-functional theory and another that includes collisions in the relaxation of the stress tensor. The introduction of a density functional-theory closure ensures self-consistency in the equation-of-state properties of the plasma (ideal and excess pressure, electric fields, and correlations). The resulting generalized hydrodynamics thus includes all impacts of Coulomb coupling, viscous damping, and the high-frequency (viscoelastic) response. We compare our results with those of several known models, including generalized hydrodynamic theory and models obtained using the Singwi-Tosi-Land-Sjolander approximation and the quasilocalized charge approximation. We find that the viscoelastic response, including both the high-frequency elastic generalization and viscous wave damping, is important for correctly describing ion-acoustic waves. We illustrate this result by considering three very different systems: ultracold plasmas, dusty plasmas, and dense plasmas. The new model is validated by comparing its results with those of the current autocorrelation function obtained from molecular-dynamics simulations of Yukawa plasmas, and the agreement is excellent. Generalizations of this model to mixtures and quantum systems should be straightforward. PMID:26274294
Sprenger, Lisa, E-mail: Lisa.Sprenger@tu-dresden.de; Lange, Adrian; Odenbach, Stefan [Institute of Fluid Mechanics, Chair of Magnetofluiddynamics, Measuring and Automation Technology, TU Dresden, 01062 Dresden (Germany)
2013-12-15
Ferrofluids are colloidal suspensions consisting of magnetic nanoparticles dispersed in a carrier liquid. Their thermodiffusive behaviour is rather strong compared to molecular binary mixtures, leading to a Soret coefficient (S{sub T}) of 0.16?K{sup ?1}. Former experiments with dilute magnetic fluids have been done with thermogravitational columns or horizontal thermodiffusion cells by different research groups. Considering the horizontal thermodiffusion cell, a former analytical approach has been used to solve the phenomenological diffusion equation in one dimension assuming a constant concentration gradient over the cell's height. The current experimental work is based on the horizontal separation cell and emphasises the comparison of the concentration development in different concentrated magnetic fluids and at different temperature gradients. The ferrofluid investigated is the kerosene-based EMG905 (Ferrotec) to be compared with the APG513A (Ferrotec), both containing magnetite nanoparticles. The experiments prove that the separation process linearly depends on the temperature gradient and that a constant concentration gradient develops in the setup due to the separation. Analytical one dimensional and numerical three dimensional approaches to solve the diffusion equation are derived to be compared with the solution used so far for dilute fluids to see if formerly made assumptions also hold for higher concentrated fluids. Both, the analytical and numerical solutions, either in a phenomenological or a thermodynamic description, are able to reproduce the separation signal gained from the experiments. The Soret coefficient can then be determined to 0.184?K{sup ?1} in the analytical case and 0.29?K{sup ?1} in the numerical case. Former theoretical approaches for dilute magnetic fluids underestimate the strength of the separation in the case of a concentrated ferrofluid.
General formulation of transverse hydrodynamics
Ryblewski, Radoslaw [Institute of Physics, Jan Kochanowski University, PL-25406 Kielce (Poland); Florkowski, Wojciech [Institute of Physics, Jan Kochanowski University, PL-25406 Kielce (Poland); H. Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Krakow (Poland)
2008-06-15
General formulation of hydrodynamics describing transversally thermalized matter created at the early stages of ultrarelativistic heavy-ion collisions is presented. Similarities and differences with the standard three-dimensionally thermalized relativistic hydrodynamics are discussed. The role of the conservation laws as well as the thermodynamic consistency of two-dimensional thermodynamic variables characterizing transversally thermalized matter is emphasized.
Elemental mechanisms of hydrodynamic instabilities
D. Y. Hsieh
1994-01-01
The elemental mechanisms for many hydrodynamic instabilities can be identified as negative damping, negative diffusion or\\u000a ellipticity. Identifications of some well-known hydrodynamic instabilities are made. Model equations in connection with the\\u000a instability associated with ellipticity should be studied more extensively.
Lifshitz Superfluid Hydrodynamics
Shira Chapman; Carlos Hoyos; Yaron Oz
2014-10-09
We construct the first order hydrodynamics of quantum critical points with Lifshitz scaling and a spontaneously broken symmetry. The fluid is described by a combination of two flows, a normal component that carries entropy and a super-flow which has zero viscosity and carries no entropy. We analyze the new transport effects allowed by the lack of boost invariance and constrain them by the local second law of thermodynamics. Imposing time-reversal invariance, we find eight new parity even transport coefficients. The formulation is applicable, in general, to any superfluid/superconductor with an explicit breaking of boost symmetry, in particular to high $T_c$ superconductors. We discuss possible experimental signatures.
Hydrodynamic effects on coalescence.
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
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.
Lifshitz Superfluid Hydrodynamics
Chapman, Shira; Oz, Yaron
2014-01-01
We construct the first order hydrodynamics of quantum critical points with Lifshitz scaling and a spontaneously broken symmetry. The fluid is described by a combination of two flows, a normal component that carries entropy and a super-flow which has zero viscosity and carries no entropy. We analyze the new transport effects allowed by the lack of boost invariance and constrain them by the local second law of thermodynamics. Imposing time-reversal invariance, we find eight new parity even transport coefficients. The formulation is applicable, in general, to any superfluid/superconductor with an explicit breaking of boost symmetry, in particular to high $T_c$ superconductors. We discuss possible experimental signatures.
Dynamics of Generalized Hydrodynamics: Hyperbolic and Pseudohyperbolic Burgers Equations
Carlos Escudero
2009-12-14
The equations of continuum hydrodynamics can be derived from the Boltzmann equation, which describes rarefied gas dynamics at the kinetic level, by means of the Chapman-Enskog expansion. This expansion assumes a small Knudsen number, and as a consequence, the hydrodynamics equations are able to successfully describe sound propagation when the frequency of a sound wave is much higher than the collision frequency of the particles. When both frequencies become comparable, these equations give a poor account of the experimental measurements. A series of generalized hydrodynamic equations has been introduced in the literature along the years in order to improve the continuous description of small scale properties of fluid flow, as ultrasound propagation. We will describe herein some of the simplified models that has been proposed so far.
On the choice of random wave simulation in the surf zone processes
Yuan, Jing
2010-01-01
In this paper, the two common approaches to account for wave randomness, the spectral approach and the wave-by-wave approach, are compared through numerical experiments conducted with the coupling of a surf zone hydrodynamic ...
Influence of large size magnetic particles on the magneto-viscous properties of ferrofluid
NASA Astrophysics Data System (ADS)
Shah, Kruti; Upadhyay, R. V.; Aswal, V. K.
2012-07-01
We compare the magneto-viscous behavior in a shear flow of three different types of magnetic suspension in the presence of a magnetic field. The first suspension contains magnetite particles of average size 10 nm dispersed in transformer oil. The second one is made of large sized magnetite particles having 30 nm particle size dispersed in transformer oil. The third suspension is a mixture of the first and second fluids in different weight proportions. The size and size distribution have been confirmed by transmission microscopy and small angle neutron scattering experiments. The rheological properties of the first two suspensions were measured for varying shear and field values. The flow behavior of the nanosized dispersed ferrofluid is described with Bingham’s yield stress model and it varied from 2.2 to 5.5 Pa on increasing the field from 0 to 1 T. The large sized particle dispersed fluid exhibits magneto-viscous behavior with increasing field. The value of Bingham’s yield stress obtained is nearly 15 times higher than that of the small size dispersion. On mixing these two fluids with different weight fractions, the Bingham yield stress value increases by a factor of three compared with that of the large sized particle dispersed fluid. The Mason number provides a good scaling of data in the steady simple flow regime. The observed yielding behavior is due to the formation of a longer chain structure in the system under the field and in-field microscopy confirms the same. The present study shows that the addition of large sized magnetic particles in magnetic fluid increases the yield stress as well as the fluid stability under a field.
Constraining relativistic viscous hydrodynamical evolution
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
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.
Jain, Dr Nirmesh [University of Sydney, Australia] [University of Sydney, Australia; Liu, Dr C K [Institute of Materials research and Engineering, A-STAR, Singapore] [Institute of Materials research and Engineering, A-STAR, Singapore; Hawkett, Dr B. S. [University of Sydney, Australia] [University of Sydney, Australia; Warr, G. G. [University of Sydney, Australia] [University of Sydney, Australia; Hamilton, William A [ORNL] [ORNL
2014-01-01
The optical magnetic chaining technique (MCT) developed by Leal-Calderon, Bibette and co-workers in the 1990 s allows precise measurements of force profiles between droplets in monodisperse ferrofluid emulsions. However, the method lacks an in-situ determination of droplet size and therefore requires the combination of separately acquired measurements of droplet chain periodicity versus an applied magnetic field from optical Bragg scattering and droplet diameter inferred from dynamic light scattering (DLS) to recover surface force-distance profiles between the colloidal particles. Compound refractive lens (CRL) focussed small-angle scattering (SANS) MCT should result in more consistent measurements of droplet size (form factor measurements in the absence of field) and droplet chaining period (from structure factor peaks when the magnetic field is applied); and, with access to shorter length scales, extend force measurements to closer approaches than possible by optical measurements. We report on CRL-SANS measurements of monodisperse ferrofluid emulsion droplets aligned in straight chains by an applied field perpendicular to the incident beam direction. Analysis of the scattering from the closely spaced droplets required algorithms that carefully treated resolution and its effect on mean scattering vector magnitudes in order to determine droplet size and chain periods to sufficient accuracy. At lower applied fields scattering patterns indicate structural correlations transverse to the magnetic field direction due to the formation of intermediate structures in early chain growth.
NASA Astrophysics Data System (ADS)
Vales-Pinzón, C.; Alvarado-Gil, J. J.; Medina-Esquivel, R.; Martínez-Torres, P.
2014-11-01
Magneto-optic phenomena in ferrofluids have been shown to be related to the formation of chain structures, due to the arrangement of the ferromagnetic particles, induced by an applied magnetic field. In this work, the effects on transmission of polarized light due to anisotropic effects induced by an external magnetic field in ferrofluids with carbon nanotubes are studied. The time response of the system presents two well defined stages, in the first one, which is very short, the fluid behaves as a polarizer. In contrast in the second stage, the effects of light transmission dominate. In this stage the transmitted light intensity grows with time and after a long time reaches a constant stable value. It is shown that these phenomena depend on the carbon nanotubes concentration as well as on the strength of the applied magnetic field. Using a simple model that considers a chain-like structure formation, it is possible to determine the rate of agglomeration of the formed structures and the attenuation coefficient of the transmitted light. The formation of nanostructures leads to variation in the transmitted light, depending on the polarization of the incident light. These magnetic nanostructures can find numerous applications in nanotechnology, optical devices and medicine.
Polarized seismic and solitary waves run-up at the sea bed
Dennis, L. C.C.; Zainal, A. A.; Faisal, S. Y. [Universiti Teknologi PETRONAS, 31750 Tronoh, Perak (Malaysia); Universiti Teknologi Malaysia, 81310 Johor Bahru (Malaysia)
2012-09-26
The polarization effects in hydrodynamics are studied. Hydrodynamic equation for the nonlinear wave is used along with the polarized solitary waves and seismic waves act as initial waves. The model is then solved by Fourier spectral and Runge-Kutta 4 methods, and the surface plot is drawn. The output demonstrates the inundation behaviors. Consequently, the polarized seismic waves along with the polarized solitary waves tend to generate dissimilar inundation which is more disastrous.
Hydrodynamics of micropipette aspiration.
Drury, J L; Dembo, M
1999-01-01
The dynamics of human neutrophils during micropipette aspiration are frequently analyzed by approximating these cells as simple slippery droplets of viscous fluid. Here, we present computations that reveal the detailed predictions of the simplest and most idealized case of such a scheme; namely, the case where the fluid of the droplet is homogeneous and Newtonian, and the surface tension of the droplet is constant. We have investigated the behavior of this model as a function of surface tension, droplet radius, viscosity, aspiration pressure, and pipette radius. In addition, we have tabulated a dimensionless factor, M, which can be utilized to calculate the apparent viscosity of the slippery droplet. Computations were carried out using a low Reynolds number hydrodynamics transport code based on the finite-element method. Although idealized and simplistic, we find that the slippery droplet model predicts many observed features of neutrophil aspiration. However, there are certain features that are not observed in neutrophils. In particular, the model predicts dilation of the membrane past the point of being continuous, as well as a reentrant jet at high aspiration pressures. PMID:9876128
Hydrodynamic delivery protocols.
Rychahou, Piotr G; Evers, B Mark
2010-01-01
RNA interference (RNAi) holds considerable promise as a novel therapeutic strategy to silence disease-causing genes not amenable to conventional therapeutics. Since it relies on small interfering RNAs (siRNAs), which are the mediators of RNAi-induced specific mRNA degradation, a major issue is the delivery of therapeutically active siRNAs into the target tissue. In vivo gene silencing with RNAi has been reported using both viral vector delivery and high-pressure, high-volume intravenous (i.v.) injection of synthetic siRNAs. For safety reasons, strategies based on viral vector delivery may be only of limited clinical use. The more desirable approach is to directly deliver active siRNAs. We describe the use of hydrodynamic administration as a technique to deliver naked siRNA constructs into experimental animals as a method of transient gene knockdown. This approach demonstrates that RNAi can be used to silence endogenous genes, involved in the cause of human diseases, with a clinically acceptable formulation and route of administration. PMID:20217552
Advanced in Macrostatistical Hydrodynamics
Graham, A.L.; Tetlow, N.; Abbott, J.R. [Los Alamos National Lab., NM (United States); Mondy, L.S. [Sandia National Labs., Albuquerque, NM (United States); Brenner, H. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Chemical Engineering
1993-08-01
An overview is presented of research that focuses on slow flows of suspensions in which colloidal and inertial effects are negligibly small (Macrostatistical Hydrodynamics). First, we describe nuclear magnetic resonance imaging experiments to quantitatively measure particle migration occurring in concentrated suspensions undergoing a flow with a nonuniform shear rate. These experiments address the issue of how the flow field affects the microstructure of suspensions. In order to understand the local viscosity in a suspension with such a flow-induced, spatially varying concentration, one must know how the viscosity of a homogeneous suspension depends on such variables as solids concentration and particle orientation. We suggest the technique of falling ball viscometry, using small balls, as a method to determine the effective viscosity of a suspension without affecting the original microstructure significantly. We also describe data from experiments in which the detailed fluctuations of a falling ball`s velocity indicate the noncontinuum nature of the suspension and may lead to more insights into the effects of suspension microstructure on macroscopic properties. Finally, we briefly describe other experiments that can be performed in quiescent suspensions (in contrast to the use of conventional shear rotational viscometers) in order to learn more about the microstructure and boundary effects in concentrated suspensions.
Relativistic Hydrodynamics on Graphic Cards
Jochen Gerhard; Volker Lindenstruth; Marcus Bleicher
2012-09-09
We show how to accelerate relativistic hydrodynamics simulations using graphic cards (graphic processing units, GPUs). These improvements are of highest relevance e.g. to the field of high-energetic nucleus-nucleus collisions at RHIC and LHC where (ideal and dissipative) relativistic hydrodynamics is used to calculate the evolution of hot and dense QCD matter. The results reported here are based on the Sharp And Smooth Transport Algorithm (SHASTA), which is employed in many hydrodynamical models and hybrid simulation packages, e.g. the Ultrarelativistic Quantum Molecular Dynamics model (UrQMD). We have redesigned the SHASTA using the OpenCL computing framework to work on accelerators like graphic processing units (GPUs) as well as on multi-core processors. With the redesign of the algorithm the hydrodynamic calculations have been accelerated by a factor 160 allowing for event-by-event calculations and better statistics in hybrid calculations.
Hydrodynamic synchronization of colloidal oscillators
Kotar, Jurij; Leoni, Marco; Bassetti, Bruno; Lagomarsino, Marco Cosentino; Cicuta, Pietro
2010-01-01
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. PMID:20385848
Weijgaert, Rien van de
;14/03/2014 3 Kayak Surfing on ocean gravity waves Oregon Coast Waves: sea & ocean waves #12;14/03/2014 4 Sound Waves Sound Waves: #12;14/03/2014 5 Sound Waves Linear Waves Sound Waves compression rarefaction #12 are inevitable if sound waves propagate over long distances; 4. Shocks always occur when a flow hits an obstacle
A hybrid Godunov method for radiation hydrodynamics
Sekora, Michael D.; Stone, James M.
2010-09-20
From a mathematical perspective, radiation hydrodynamics can be thought of as a system of hyperbolic balance laws with dual multiscale behavior (multiscale behavior associated with the hyperbolic wave speeds as well as multiscale behavior associated with source term relaxation). With this outlook in mind, this paper presents a hybrid Godunov method for one-dimensional radiation hydrodynamics that is uniformly well behaved from the photon free streaming (hyperbolic) limit through the weak equilibrium diffusion (parabolic) limit and to the strong equilibrium diffusion (hyperbolic) limit. Moreover, one finds that the technique preserves certain asymptotic limits. The method incorporates a backward Euler upwinding scheme for the radiation energy density E{sub r} and flux F{sub r} as well as a modified Godunov scheme for the material density {rho}, momentum density m, and energy density E. The backward Euler upwinding scheme is first-order accurate and uses an implicit HLLE flux function to temporally advance the radiation components according to the material flow scale. The modified Godunov scheme is second-order accurate and directly couples stiff source term effects to the hyperbolic structure of the system of balance laws. This Godunov technique is composed of a predictor step that is based on Duhamel's principle and a corrector step that is based on Picard iteration. The Godunov scheme is explicit on the material flow scale but is unsplit and fully couples matter and radiation without invoking a diffusion-type approximation for radiation hydrodynamics. This technique derives from earlier work by Miniati and Colella (2007) . Numerical tests demonstrate that the method is stable, robust, and accurate across various parameter regimes.
Eightfold Classification of Hydrodynamic Dissipation
NASA Astrophysics Data System (ADS)
Haehl, Felix M.; Loganayagam, R.; Rangamani, Mukund
2015-05-01
We provide a complete characterization of hydrodynamic transport consistent with the second law of thermodynamics at arbitrary orders in the gradient expansion. A key ingredient in facilitating this analysis is the notion of adiabatic hydrodynamics, which enables isolation of the genuinely dissipative parts of transport. We demonstrate that most transport is adiabatic. Furthermore, in the dissipative part, only terms at the leading order in gradient expansion are constrained to be sign definite by the second law (as has been derived before).
Eightfold Classification of Hydrodynamic Dissipation.
Haehl, Felix M; Loganayagam, R; Rangamani, Mukund
2015-05-22
We provide a complete characterization of hydrodynamic transport consistent with the second law of thermodynamics at arbitrary orders in the gradient expansion. A key ingredient in facilitating this analysis is the notion of adiabatic hydrodynamics, which enables isolation of the genuinely dissipative parts of transport. We demonstrate that most transport is adiabatic. Furthermore, in the dissipative part, only terms at the leading order in gradient expansion are constrained to be sign definite by the second law (as has been derived before). PMID:26047219
Purely hydrodynamic origin for swarming of swimming particles
Norihiro Oyama; John Jairo Molina; Ryoichi Yamamoto
2015-06-04
Understanding the process of group formation, from individual dynamics to collective motion, is a key issue in biology. However, we still do not fully understand the underlying mechanisms behind the complex collective behaviours seen even in very simple systems, such as crawling cells or swimming bacteria. In this work, three-dimensional simulations with fully resolved hydrodynamics are performed to study the collective motion of model swimming particles in confinement. We show that certain swimming mechanisms can lead to travelling wave-like collective motion even without any direct alignment mechanism. It is also shown that by varying the swimming mechanism, this collective motion can be suppressed, contrary to the perception that hydrodynamic effects are completely screened. From an analysis of bulk systems, it is shown that this travelling wave-like motion, which can be characterized as a pseudo-acoustic mode, is mainly due to the intrinsic property of the swimmers.
Simulation of astrophysical jet using the special relativistic hydrodynamics code
Orhan Donmez; Refik Kayali
2006-02-14
This paper describes a multidimensional hydrodynamic code which can be used for the studies of relativistic astrophysical flows. The code solves the special relativistic hydrodynamic equations as a hyperbolic system of conservation laws based on High Resolution Shock Capturing (HRSC) Scheme. Two standard tests, one of which is the relativistic blast wave tested in our previous paper\\cite{DO1}, and the other is the collision of two ultrarelativistic blast waves tested in here, are presented to demonstrate that the code captures correctly and gives solution in the discontinuities, accurately. The relativistic astrophysical jet is modeled for the ultrarelativistic flow case. The dynamics of jet flowing is then determined by the ambient parameters such as densities, and velocities of the jets and the momentum impulse applied to the computational surface. We obtain solutions for the jet structure, propagation of jet during the time evolution, and variation in the Mach number on the computational domain at a fixed time.
Quantum hydrodynamics: capturing a reactive scattering resonance.
Derrickson, Sean W; Bittner, Eric R; Kendrick, Brian K
2005-08-01
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
Vegetation Hydrodynamics - Recent Developments and Future Challenges
NASA Astrophysics Data System (ADS)
Nepf, H. M.
2014-12-01
For over a century vegetation has been removed from channels and coastal zones to facilitate navigation and development. In recent decades, however, we have recognized the ecologic and economic benefits of aquatic vegetation. It buffers against coastal eutrophication, damps waves and coastal storm surge, provides habitat, inhibits bank erosion, and provides significant carbon storage. The management of watersheds and coastal zones has turned from vegetation removal to restoration. In the past 20 years, the study of vegetation hydrodynamics has accelerated to meet the need to understand feedbacks between vegetation, flow and sediment transport. This presentation will describe key features of vegetation hydrodynamics, first at the meadow scale and then at the scale of individual patches, examining how vegetation density and meadow (or patch) morphology impact flow, with subsequent implications for sediment fate. Finally, the talk highlights differences in turbulence generation between bare and vegetated beds that may limit the transfer of open channel sediment transport models to vegetated channels, creating the future challenge of defining sediment transport models appropriate for vegetated regions.
Analytical Solutions of Landau (1+1)-Dimensional Hydrodynamics
Sen, Abhisek; Gerhard, Jochen; Torrieri, Giorgio; Read Jr, Kenneth F
2014-01-01
To help guide our intuition, summarize important features, and point out essential elements, we review the analytical solutions of Landau (1+1)-dimensional hydrodynamics and exhibit the full evolution of the dynamics from the very beginning to subsequent times. Special emphasis is placed on the matching and the interplay between the Khalatnikov solution and the Riemann simple wave solution at the earliest times and in the edge regions at later times.
Hamiltonian Hydrodynamics and Irrotational Binary Inspiral
Charalampos M. Markakis
2014-10-28
Gravitational waves from neutron-star and black-hole binaries carry valuable information on their physical properties and probe physics inaccessible to the laboratory. Although development of black-hole gravitational-wave templates in the past decade has been revolutionary, the corresponding work for double neutron-star systems has lagged. Neutron stars can be well-modelled as simple barotropic fluids during the part of binary inspiral most relevant to gravitational wave astronomy, but the crucial geometric and mathematical consequences of this simplification have remained computationally unexploited. In particular, Carter and Lichnerowicz have described barotropic fluid motion via classical variational principles as conformally geodesic. Moreover, Kelvin's circulation theorem implies that initially irrotational flows remain irrotational. Applied to numerical relativity, these concepts lead to novel Hamiltonian or Hamilton-Jacobi schemes for evolving relativistic fluid flows. Hamiltonian methods can conserve not only flux, but also circulation and symplecticity, and moreover do not require addition of an artificial atmosphere typically required by standard conservative methods. These properties can allow production of high-precision gravitational waveforms at low computational cost. This canonical hydrodynamics approach is applicable to a wide class of problems involving theoretical or computational fluid dynamics.
The hydrodynamics of water strider locomotion.
Hu, David L; Chan, Brian; Bush, John W M
2003-08-01
Water striders Gerridae are insects of characteristic length 1 cm and weight 10 dynes that reside on the surface of ponds, rivers, and the open ocean. Their weight is supported by the surface tension force generated by curvature of the free surface, and they propel themselves by driving their central pair of hydrophobic legs in a sculling motion. Previous investigators have assumed that the hydrodynamic propulsion of the water strider relies on momentum transfer by surface waves. This assumption leads to Denny's paradox: infant water striders, whose legs are too slow to generate waves, should be incapable of propelling themselves along the surface. We here resolve this paradox through reporting the results of high-speed video and particle-tracking studies. Experiments reveal that the strider transfers momentum to the underlying fluid not primarily through capillary waves, but rather through hemispherical vortices shed by its driving legs. This insight guided us in constructing a self-contained mechanical water strider whose means of propulsion is analogous to that of its natural counterpart. PMID:12904790
Phonon hydrodynamics in two-dimensional materials
NASA Astrophysics Data System (ADS)
Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola
2015-03-01
The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane.
Toward a hydrodynamic theory of sonoluminescence
Loefstedt, R.; Barber, B.P.; Putterman, S.J. )
1993-11-01
For small Mach numbers the Rayleigh--Plesset equations (modified to include acoustic radiation damping) provide the hydrodynamic description of a bubble's breathing motion. Measurements are presented for the bubble radius as a function of time. They indicate that in the presence of sonoluminescence the ratio of maximum to minimum bubble radius is about 100. Scaling laws for the maximum bubble radius and the temperature and duration of the collapse are derived in this limit. Inclusion of mass diffusion enables one to calculate the ambient radius. For audible sound fields these equations yield picosecond hot spots, such as are observed experimentally. However, the analysis indicates that a detailed description of sonoluminescence requires the use of parameters for which the resulting motion reaches large Mach numbers. Therefore the next step toward explaining sonoluminescence will require the extension of bubble dynamics to include nonlinear effects such as shock waves.
Proportional Paths, Barodesy, and Granular Solid Hydrodynamics
Yimin Jiang; Mario Liu
2012-12-16
Propotional paths as summed up by the Goldscheider Rule (GR) -- stating that given a constant strain rate, the evolution of the stress maintains the ratios of its components -- is a characteristics of elasto-plastic motion in granular media. Barodesy, a constitutive relation proposed recently by Kolymbas, is a model that, with GR as input, successfully accounts for data from soil mechanical experiments. Granular solid hydrodynamics (GSH), a theory derived from general principles of physics and two assumptions about the basic behavior of granular media, is constructed to qualitatively account for a wide range of observation -- from elastic waves over elasto-plastic motion to rapid dense flow. In this paper, showing the close resemblance of results from Barodesy and GSH, we further validate GSH and provide an understanding for GR.
A new hydrodynamic analysis of double layers
NASA Technical Reports Server (NTRS)
Hora, Heinrich
1987-01-01
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.
Hydrodynamics of fingering instabilities in dipolar fluids
NASA Astrophysics Data System (ADS)
Jackson, David P.; Goldstein, Raymond E.; Cebers, Andrejs O.
1994-07-01
Domains of magnetic and electric dipolar fluids are known to undergo fingering instabilities in Hele-Shaw flow, forming complex labyrinthine patterns. The hydrodynamics of this process are studied theoretically with a generalization of Darcy's law. The boundary condition on the pressure at the interface between the dipolar fluid and that surrounding it is shown to include competing Young-Laplace and Biot-Savart terms. The spectrum of growth rates in the linear stability analysis of a circular domain has a complicated wave vector dependence as a consequence of the long-range forces, and reveals that the fingering arises from a negative effective surface tension. The free boundary problem for the interface motion is solved numerically using conformal mapping methods, and is compared with experiment. A simple model is proposed for mode competition and pattern selection under time-dependent magnetic fields. Aspects of this analysis may be relevant to the description of the intermediate state of type-I superconductors.
Hydrodynamics of coalescing binary neutron stars: Ellipsoidal treatment
NASA Technical Reports Server (NTRS)
Lai, Dong; Shapiro, Stuart L.
1995-01-01
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.
Corrugation instabilities of the Riemann problem in relativistic hydrodynamics
Patryk Mach
2011-04-19
Corrugation instabilities occurring for solutions of the Riemann problem in relativistic hydrodynamics in which the fluid moves with a non-zero velocity tangent to the initial discontinuity are studied numerically. We perform simulations both for ultrarelativistic and perfect gas equations of state. We focus on a set of problems with moderately relativistic velocities but exhausting all possible wave patterns of solutions. Perturbations are applied to the shape of the initial discontinuity. Instabilities that develop are only restricted to a region around a contact discontinuity. Both shock and rarefaction waves appear to be stable.
Yamamoto, Naoki
2015-01-01
We study the hydrodynamic regime of chiral plasmas at high temperature. We find a new type of gapless collective excitation induced by chiral effects in an external magnetic field. This is a transverse wave and is present even in incompressible fluids, unlike the chiral magnetic and chiral vortical waves. The velocity is proportional to the coefficient of the gravitational anomaly. We briefly discuss possible relevance of this "chiral Alfv\\'en wave" in physical systems.
Hydrodynamic Stability of Liquid-Propellant Combustion: Landau's Problem Revisited
NASA Technical Reports Server (NTRS)
Margolis, S. B.
2001-01-01
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.
Group-invariant solutions of hydrodynamics and radiation hydrodynamics
Coggeshall, S.V.
1993-08-01
Using the property of invariance under Lie groups of transformations, the equations of hydrodynamics are transformed from partial differential equations to ordinary differential equations, for which special analytic solutions can be found. These particular solutions can be used for (1) numerical benchmarks, (2) the basis for analytic models, and (3) insight into more general solutions. Additionally, group transformations can be used to construct new solutions from existing ones. A space-time projective group is used to generate complicated solutions from simpler solutions. Discussion of these procedures is presented along with examples of analytic of 1,2 and 3-D hydrodynamics.
1.138J / 2.062J Wave Propagation, Fall 2000
Mei, Chiang C.
Linearized theory of wave phenomena in applied mechanics. Examples are chosen from elasticity, acoustics, geophysics, hydrodynamics and other subjects. Basic concepts. One dimensional examples. Characteristics, dispersion ...
NASA Astrophysics Data System (ADS)
Krupka, Jerzy
2015-09-01
Few resonance cavities operating on different modes have been used for the accurate multi-frequency determination of the complex permittivity of highly concentrated aqueous NaCl solutions at a frequency range of 2.5?GHz to 24?GHz. It has been shown that the use of the perturbation method would lead to significant measurement uncertainties especially for lossy samples and should be avoided especially for TE0n1 mode cavities. At frequencies that are smaller than 15?GHz the imaginary part of the permittivity of NaCl solutions increases while at frequencies larger than 15?GHz it decreases, with the increasing conductivity of the electrolyte. In the last case the total dielectric losses for the saturated electrolyte are noticeably smaller than for pure water. The complex permittivity and complex permeability of ferrofluid, liquid that exhibits diamagnetic properties at microwave frequencies, were measured by employing two cylindrical cavities operating on complementary modes.
NASA Astrophysics Data System (ADS)
Zeng, Jian; Deng, Yanxiang; Vedantam, Pallavi; Tzeng, Tzuen-Rong; Xuan, Xiangchun
2013-11-01
The separation of particles and cells is critical in many chemical and biological applications. This work presents a simple idea for utilizing a pair of permanent magnets to continuously separate diamagnetic particles and cells in ferrofluid flow through a straight microchannel. The first magnet is placed close to the microchannel for focusing the particle mixture to a single stream without the use of a sheath flow. The second magnet, which is offset from the first magnet and placed farther from the channel, is to displace the aligned particles to dissimilar flow paths for a continuous sorting. This idea is first demonstrated through the separation of 3 ?m- and 10 ?m-diameter polystyrene particles, where the effects of flow speed and magnet distance are both examined. The experimental data are found to fit well with the predictions of an analytical model. Furthermore, a continuous separation of live yeast cells from 10 ?m polystyrene particles is implemented in the same device.
What Controls the Hydrodynamics of the Central Congo River?
NASA Astrophysics Data System (ADS)
O'Loughlin, F.; Bates, P. D.
2014-12-01
Despite being the second largest river basin in the world, with a drainage area greater than 3.7 million square kilometres, little is known about the hydraulics of the Congo River. This lack of knowledge is mainly due to a mixture of conflicts and the difficulty of accessing existing data. We present results of studies which have focused primarily on the middle reach of the Congo River, located between Kisangani and Kinshasa, and its six main tributaries (Kasai, Ubangai, Sangha, Ruki, Lulonga and Lomami rivers). Through a combination of remotely sensed datasets and a hydrodynamic model we investigated what factors control the hydrodynamics of the middle reach. From the analysis of the remotely sensed datasets, we discover that variability in river width of the middle reach of the Congo is large and cannot be represented by empirical equations which relate channel geometry to basin area and discharge. Water surface slopes vary from 3.5 cm/km to 9 cm/km, which is far more than previous studies suggest. The remote datasets indicate that there exist 5 large constrictions in the river width which may result in backwater affecting between 11 and 33 percent of middle reach at low and high water respectively. These results were corroborated by the hydrodynamic model. In fact, when all constrictions caused by a narrowing in width of 1 km or more are considered, water levels along 43 percent of the middle reach change by at least 0.5 m. Using the hydrodynamic model we also investigated the importance of the wetlands to the attenuation of the flood wave through the system. Initial results suggest that for the Congo River, floodplains have far more impact on the peak magnitude than the timing of the flood wave. When the model was run with no floodplain interactions an increase in the magnitude of flood peak was observed, with the timing of the waves being consistent with observed measurements.
Abnormal pressures as hydrodynamic phenomena
Neuzil, C.E.
1995-01-01
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
Isogeometric analysis of Lagrangian hydrodynamics
NASA Astrophysics Data System (ADS)
Bazilevs, Y.; Akkerman, I.; Benson, D. J.; Scovazzi, G.; Shashkov, M. J.
2013-06-01
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.
Hydrodynamics of fractal continuum flow
NASA Astrophysics Data System (ADS)
Balankin, Alexander S.; Elizarraraz, Benjamin Espinoza
2012-02-01
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.
Hydrodynamic interactions in protein folding
NASA Astrophysics Data System (ADS)
Cieplak, Marek; Niewieczerza?, Szymon
2009-03-01
We incorporate hydrodynamic interactions (HIs) in a coarse-grained and structure-based model of proteins by employing the Rotne-Prager hydrodynamic tensor. We study several small proteins and demonstrate that HIs facilitate folding. We also study HIV-1 protease and show that HIs make the flap closing dynamics faster. The HIs are found to affect time correlation functions in the vicinity of the native state even though they have no impact on same time characteristics of the structure fluctuations around the native state.
NASA Astrophysics Data System (ADS)
Cuppo, F. L. S.; Gómez, S. L.; Figueiredo Neto, A. M.
2004-04-01
In this paper is reported a systematic experimental study of the linear-optical-absorption coefficient of ferrofluid-doped isotropic lyotropic mixtures as a function of the magnetic-grains concentration. The linear optical absorption of ferrolyomesophases increases in a nonlinear manner with the concentration of magnetic grains, deviating from the usual Beer-Lambert law. This behavior is associated to the presence of correlated micelles in the mixture which favors the formation of small-scale aggregates of magnetic grains (dimers), which have a higher absorption coefficient with respect to that of isolated grains. We propose that the indirect heating of the micelles via the ferrofluid grains (hyperthermia) could account for this nonlinear increase of the linear-optical-absorption coefficient as a function of the grains concentration.
NASA Astrophysics Data System (ADS)
Hennenberg, M.; Slavtchev, S.; Valchev, G.
2013-12-01
When an isothermal ferrofluid is submitted to an oscillating magnetic field, the initially motionless liquid free surface can start to oscillate. This physical phenomenon is similar to the Faraday instability for usual Newtonian liquids subjected to a mechanical oscillation. In the present paper, we consider the magnetic field as a sum of a constant part and a time periodic part. Two different cases for the constant part of the field, being vertical in the first one or horizontal in the second one are studied. Assuming both ferrofluid magnetization and magnetic field to be collinear, we develop the linear stability analysis of the motionless reference state taking into account the Kelvin magnetic forces. The Laplace law describing the free surface deformation reduces to Hill's equation, which is studied using the classical method of Ince and Erdelyi. Inside this framework, we obtain the transition conditions leading to the free surface oscillations.
Simulation of seismic signals from asymmetric LANL hydrodynamic calculations
Stevens, J.L.; Rimer, N.; Halda, E.J.; Barker, T.G.; Davis, C.G.; Johnson, W.E.
1993-11-01
Hydrodynamic calculations of an asymmetric nuclear explosion source were propagated to teleseismic distances to investigate the effects of the asymmetric source on seismic signals. The source is an explosion in a 12 meter long canister with the device at one end of the canister and a metal plate adjacent to the explosion. This produces a strongly asymmetric two-lobed source in the hydrodynamic region. The hydrodynamic source is propagated to the far field using a three-step process. The Eulerian hydrodynamic code SOIL was used by LANL to calculate the material velocity, density, and internal energy up to a time of 8.9 milliseconds after the explosion. These quantities were then transferred to an initial grid for the Lagrangian elastic/plastic finite difference code CRAM, which was used by S-CUBED to propagate the signal through the region of nonlinear deformation into the external elastic region. The cavity size and shape at the time of the overlay were determined by searching for a rapid density change in the SOIL grid, and this interior region was then rezoned into a single zone. The CRAM calculation includes material strength and gravity, and includes the effect of the free surface above the explosion. Finally, far field body waves were calculated by integrating over a closed surface in the elastic region and using the representation theorem. A second calculation was performed using an initially spherical source for comparison with the asymmetric calculation.
Spin current evolution in the separated spin-up and spin-down quantum hydrodynamics
NASA Astrophysics Data System (ADS)
Trukhanova, Mariya, Iv.
2015-10-01
We have developed a method of quantum hydrodynamics (QHD) that describes particles with spin-up and with spin-down in separate. We have derived the equation of the spin current evolution as a part of the set of the quantum hydrodynamics equations that treat particles with different projection of spin on the preferable direction as two different species. We have studied orthogonal propagation of waves in the external magnetic field and determined the contribution of quantum corrections due to the Bohm potential and to magnetization energy of particles with different projections of spin in the spin-current wave dispersion. We have analyzed the limits of weak and strong magnetic fields.
NASA Astrophysics Data System (ADS)
Sunil; Sharma, Poonam; Mahajan, Amit
2010-12-01
This paper presents a nonlinear stability analysis of a double-diffusive convection in a magnetized ferrofluid layer confined between stress-free boundaries using a thermal non-equilibrium model by the energy method. A Darcy-Brinkman model is used for the momentum equation and a two-field model is used for the energy equation, each representing the solid and fluid phases separately. The mathematical emphasis is on how to control the nonlinear terms caused by magnetic body and inertia forces. The effects of the interface heat transfer coefficient ( {{\\ H}^\\prime } ) , magnetic parameter (M3), Darcy-Brinkman number ( {\\hat{D}a} ) and porosity-modified conductivity ratio (?') on the onset of ferroconvection in the presence of solute (S') have been analysed. For all the cases studied, it is found that solute gradient enhances the stability of the system. A comparison with linear instability theory shows that there is a difference between the critical Rayleigh numbers and thus indicates the possibility of the existence of a subcritical instability region for ferrofluids. However, for non-ferrofluids stability and instability boundaries coincide.
From Field Theory to the Hydrodynamics of Relativistic Superfluids
Stephan Stetina
2015-01-31
The hydrodynamic description of a superfluid is usually based on a two-fluid picture. In this thesis, basic properties of such a relativistic two-fluid system are derived from the underlying microscopic physics of a complex scalar quantum field theory. To obtain analytic results of all non-dissipative hydrodynamic quantities in terms of field theoretic variables, calculations are first carried out in a low-temperature and weak-coupling approximation. In a second step, the 2-particle-irreducible formalism is applied: This formalism allows for a numerical evaluation of the hydrodynamic parameters for all temperatures below the critical temperature. In addition, a system of two coupled superfluids is studied. As an application, the velocities of first and second sound in the presence of a superflow are calculated. The results show that first (second) sound evolves from a density (temperature) wave at low temperatures to a temperature (density) wave at high temperatures. This role reversal is investigated for ultra-relativistic and near-nonrelativistic systems for zero and nonzero superflow. The studies carried out in this thesis are of a very general nature as one does not have to specify the system for which the microscopic field theory is an effective description. As a particular example, superfluidity in dense quark and nuclear matter in compact stars are discussed.
Hydrodynamic instabilities in inertial fusion
Hoffman, N.M.
1994-09-01
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.
Hydrodynamically mediated macrophyte silica dynamics.
Schoelynck, J; Bal, K; Puijalon, S; Meire, P; Struyf, E
2012-11-01
In most aquatic ecosystems, hydrodynamic conditions are a key abiotic factor determining species distributions and abundance of aquatic plants. Resisting stress and keeping an upright position often relies on investment in tissue reinforcement, which is costly to produce. Silica could provide a more economical alternative. Two laboratory experiments were conducted to measure the response of two submerged species, Egeria densa Planch. and Limnophila heterophylla (Roxb.) Benth., to dissolved silicic acid availability and exposure to hydrodynamic stress. The results were verified with a third species in a field study (Nuphar lutea (L.) Smith). Biogenic silica (BSi) concentration in both stems and leaves increases with increasing dissolved silica availability but also with the presence of hydrodynamic stress. We suggest that the inclusion of extra silica enables the plant to alternatively invest its energy in the production of lignin and cellulose. Although we found no significant effects of hydrodynamic stress on cellulose or lignin concentrations either in the laboratory or in the field, BSi was negatively correlated with cellulose concentration and positively correlated with lignin concentration in samples collected in the field study. This implies that the plant might perform with equal energy efficiency in both standing and running water environments. This could provide submerged species with a tool to respond to abiotic factors, to adapt to new ecological conditions and hence potentially colonise new environments. PMID:22512916
Beyond Hydrodynamics by Dynamical NEMD
Roma "La Sapienza", Università di
Beyond Hydrodynamics by Dynamical NEMD G.Ciccotti Dpt. of Physics, Univ. of Rome "La Sapienza" and School of Physics, UCD, Dublin With S. Meloni (Dublin) S. Orlandini (Rome) M.L. Mugnai (Austin) C. Pierleoni (Rome) S. Caprara (Rome) M. Mareschal (Brussels) ·Equilibrium vs NEMD ·Average in NEMD (Onsager
Meat Products, Hydrodynamic Pressure Processing
Technology Transfer Automated Retrieval System (TEKTRAN)
The hydrodynamic pressure process (HDP) has been shown to be very effective at improving meat tenderness in a variety of meat cuts. When compared to conventional aging for tenderization, HDP was more effective. The HDP process may offer the meat industry a new alternative for tenderizing meat in add...
Millifluidics: Capillarity and Interfacial Hydrodynamics
Bico,José
;"Lotus" effect Setcreasea Natural water-repellent surfaces: some plant leaves insect wings water spidersMillifluidics: Capillarity and Interfacial Hydrodynamics 1: Surface tension: the basics 2: Liquid the liquid 4.2 Super-hydrophobic surfaces 4. Actual surfaces #12;!* $LV $SV$SL ** %S = top of asperities
Dynamical Spacetimes from Numerical Hydrodynamics
Allan Adams; Nathan Benjamin; Arvin Moghaddam; Wojciech Musial
2014-11-07
We numerically construct dynamical asymptotically-AdS$_4$ metrics by evaluating the fluid/gravity metric on numerical solutions of dissipative hydrodynamics in (2+1) dimensions. The resulting numerical metrics satisfy Einstein's equations in (3+1) dimensions to high accuracy.
Smoothed Particle Hydrodynamics Stability Analysis
J. W. Swegle; D. L. Hicks; S. W. Attaway
1995-01-01
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
A hydrodynamic approach to non-equilibrium conformal field theories
Bernard, Denis
2015-01-01
We develop a hydrodynamic approach to non-equilibrium conformal field theory. We study non-equilibrium steady states in the context of one-dimensional conformal field theory perturbed by the $T\\bar T$ irrelevant operator. By direct quantum computation, we show, to first order in the coupling, that a relativistic hydrodynamic emerges, which is a simple modification of one-dimensional conformal fluids. We show that it describes the steady state and its approach, and we provide the main characteristics of the steady state, which lies between two shock waves. The velocities of these shocks are modified by the perturbation and equal the sound velocities of the asymptotic baths. Pushing further this approach, we are led to conjecture that the approach to the steady state is generically controlled by the power law $t^{-1/2}$, and that the widths of the shocks increase with time according to $t^{1/3}$.
A hydrodynamic approach to non-equilibrium conformal field theories
Denis Bernard; Benjamin Doyon
2015-07-27
We develop a hydrodynamic approach to non-equilibrium conformal field theory. We study non-equilibrium steady states in the context of one-dimensional conformal field theory perturbed by the $T\\bar T$ irrelevant operator. By direct quantum computation, we show, to first order in the coupling, that a relativistic hydrodynamic emerges, which is a simple modification of one-dimensional conformal fluids. We show that it describes the steady state and its approach, and we provide the main characteristics of the steady state, which lies between two shock waves. The velocities of these shocks are modified by the perturbation and equal the sound velocities of the asymptotic baths. Pushing further this approach, we are led to conjecture that the approach to the steady state is generically controlled by the power law $t^{-1/2}$, and that the widths of the shocks increase with time according to $t^{1/3}$.
Hydrodynamic simulations of microjetting from shock-loaded grooves
NASA Astrophysics Data System (ADS)
Roland, Caroline; de Resseguier, Thibaut; Sollier, Arnaud; Lescoute, Emilien; Soulard, Laurent; Loison, Didier
2015-06-01
The interaction of a shock wave with a free surface presenting geometrical defects, such as cavities or grooves, may lead to the ejection of micrometric debris at velocities of km/s order. This process can be involved in many applications, like pyrotechnics or industrial safety. Laser shock experiments reported in this conference (T. de Resseguier, C. Roland et al., abstract ref.000066) provide insight into jet formation and peak velocities for various groove angles and shock pressures. Here, we present hydrodynamic simulations of these experiments, in both 2D and 3D geometries, using both finite element method and smoothed particles hydrodynamics. Numerical results are compared to several theoretical predictions including the Richtmyer-Meshkov instabilities. The role of the elastic-plastic behavior on jet formation is investigated. Finally, the possibility to simulate the late stages of jet expansion and fragmentation is explored, to evaluate the mass distribution of the ejecta and their ballistic properties, still essentially unknown in the experiments.
Hydrodynamic model of Fukushima-Daiichi NPP Industrial site flooding
Vaschenko, V N; Gerasimenko, T V; Vachev, B
2014-01-01
While the Fukushima-Daiichi was designed and constructed the maximal tsunami height estimate was about 3 m based on analysis of statistical data including Chile earthquake in 1960. The NPP project industrial site height was 10 m. The further deterministic estimates TPCO-JSCE confirmed the impossibility of the industrial site flooding by a tsunami and therefore confirmed ecological safety of the NPP. However, as a result of beyond design earthquake of 11 March 2011 the tsunami height at the shore near the Fukushima-Daiichi NPP reached 15 m. This led to flooding and severe emergencies having catastrophic environmental consequences. This paper proposes hydrodynamic model of tsunami emerging and traveling based on conservative assumptions. The possibility of a tsunami wave reaching 15 m height at the Fukushima-Daiichi NPP shore was confirmed for deduced hydrodynamic resistance coefficient of 1.8. According to the model developed a possibility of flooding is determined not only by the industrial site height, magni...
Extent of validity of the hydrodynamic description of ions in dense plasmas
Mithen, James P.; Gregori, Gianluca [Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Daligault, Jerome [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2011-01-15
We show that the hydrodynamic description can be applied to modeling the ionic response in dense plasmas for a wide range of length scales that are experimentally accessible. Using numerical simulations for the Yukawa model, we find that the maximum wave number k{sub max} at which the hydrodynamic description applies is independent of the coupling strength, given by k{sub max}{lambda}s{approx_equal}0.43, where {lambda}{sub s} is the ionic screening length. Our results show that the hydrodynamic description can be used for interpreting x-ray scattering data from fourth generation light sources and high power lasers. In addition, our investigation sheds new light on how the domain of validity of the hydrodynamic description depends on both the microscopic properties and the thermodynamic state of fluids in general.
Anomalous hydrodynamics of fractional quantum Hall states
Wiegmann, P.
2013-09-15
We propose a comprehensive framework for quantum hydrodynamics of the fractional quantum Hall (FQH) states. We suggest that the electronic fluid in the FQH regime can be phenomenologically described by the quantized hydrodynamics of vortices in an incompressible rotating liquid. We demonstrate that such hydrodynamics captures all major features of FQH states, including the subtle effect of the Lorentz shear stress. We present a consistent quantization of the hydrodynamics of an incompressible fluid, providing a powerful framework to study the FQH effect and superfluids. We obtain the quantum hydrodynamics of the vortex flow by quantizing the Kirchhoff equations for vortex dynamics.
Sweetman, Bert
From Proceedings, BOSS-97: Behaviour of Offshore Structures Volume 2 (Hydrodynamics), ed. J TEST RESULTS Alok K. Jha, P. R. de Jong, and Steven R. Winterstein Civil Engineering Dept., StanfordKeywordsKeywordsKeywordsKeywordsKeywords Nonlinear wave diffraction; offshore structures; random vibration; spar buoys, structural reliability; wave
Computations of fully nonlinear three-dimensional wave-body interactions
Yan, Hongmei
2010-01-01
Nonlinear effects in hydrodynamics of wave-body interaction problems become critically important when large-amplitude body motions and/or extreme surface waves are involved. Accurate prediction and understanding of these ...
Hobensack, William Alan
1999-01-01
A physical model study was conducted in a narrow wave flume to verify a previously developed numerical model for predicting the hydrodynamic response to irregular waves on a rough impermeable slope. In the physical model study, one case was run...
Hydrodynamics of offshore structures: Mathematical theory and its applications in structures
Chakrabarti, S.K.
1987-01-01
This book covers the hydrodynamic effects of offshore structures. The subject of hydrodynamics applied to the structures is so vast that it is impossible to incorporate every aspect of this subject in one book. This monograph introduces various types of offshore structures with reference to their actual installation in various parts of the world. It describes wave mechanics and how to choose wave theories and design waves. After a choice of design is made, the resulting wave is used to calculate forces acting on a fixed offshore structure. Various methods for determining the ensuing motions of these structures are presented. Short- and long-term responses are derived, and model tests to verify these methods are carefully explained.
Inertial-Microfluidic Hydrodynamic Lens
NASA Astrophysics Data System (ADS)
Kim, Young Won; Yoo, Jung Yul
2009-11-01
A hydrodynamic lens is the methodology to focus nano- and micro-particles suspended in liquid medium. We designed and tested a single-stage inertial-microfluidic hydrodynamic lens embodied in a microchip for biomedical and environmental applications. We adopted cylindrical micro-orifices with diameters of 100--300 ?m, transporting micro-particles in sizes of 1--16 ?m. A numerical study is conducted to provide optimum design rules of the lens system. The lens performances are evaluated in terms of Stokes number considering the particle size, the orifice diameter, and the flow Reynolds number. Micro-particle tracking velocimetry (?-PTV) adopting Nd:YAG lasers, which freeze flowing particles, are applied, and compared with the numerical simulation in terms of the focused beam diameter. The particle focusing method suggested in this work is fairly simple, sheathless, and free from necessity of other external forces.
Generic Conditions for Hydrodynamic Synchronization
NASA Astrophysics Data System (ADS)
Uchida, Nariya; Golestanian, Ramin
2011-02-01
Synchronization of actively oscillating organelles such as cilia and flagella facilitates self-propulsion of cells and pumping fluid in low Reynolds number environments. To understand the key mechanism behind synchronization induced by hydrodynamic interaction, we study a model of rigid-body rotors making fixed trajectories of arbitrary shape under driving forces that are arbitrary functions of the phase. For a wide class of geometries, we obtain the necessary and sufficient conditions for synchronization of a pair of rotors. We also find a novel synchronized pattern with an oscillating phase shift. Our results shed light on the role of hydrodynamic interactions in biological systems, and could help in developing efficient mixing and transport strategies in microfluidic devices.
Hydrodynamics from Landau initial conditions
NASA Astrophysics Data System (ADS)
Sen, Abhisek; Gerhard, Jochen; Torrieri, Giorgio; Read, Kenneth; Wong, Cheuk-Yin
2015-07-01
We investigate ideal hydrodynamic evolution, with Landau initial conditions, both in a semi-analytical 1+1D approach and in a numerical code incorporating event-by event variation with many events and transverse density inhomogeneities. The object of the calculation is to test how fast would a Landau initial condition transition to a commonly used boost-invariant expansion. We show that the transition to boost-invariant flow occurs too late for realistic setups, with corrections of O (20 — 30%) expected at freeze out for most scenarios. Moreover, the deviation from boost-invariance is correlated with both transverse flow and elliptic flow, with the more highly transversely flowing regions also showing the most violation of boost invariance. Therefore, if longitudinal flow is not fully developed at the early stages of heavy ion collisions, 2+1 dimensional hydrodynamics is inadequate to extract transport coefficients of the quark-gluon plasma. Based on [1, 2
Membrane Paradigm and Holographic Hydrodynamics
Christopher Eling; Yasha Neiman; Yaron Oz
2010-12-12
We discuss recent work showing that in certain cases the membrane paradigm equations governing the dynamics of black hole horizons can be recast as relativistic conservation law equations. In the context of gauge/gravity dualities, these equations are interpreted as defining the viscous hydrodynamics of a holographically dual relativistic field theory. Using this approach, one can derive the viscous transport coefficients and the form of the entropy current for field theories dual to gravity plus matter fields.
Ion acoustic shock waves in degenerate plasmas
N. Akhtar; S. Hussain
2011-01-01
Korteweg de Vries Burgers equation for negative ion degenerate dissipative plasma has been derived using reductive perturbation technique. The quantum hydrodynamic model is used to study the quantum ion acoustic shock waves. The effects of different parameters on quantum ion acoustic shock waves are studied. It is found that quantum parameter, electrons Fermi temperature, temperature of positive and negative ions,
Particle hydrodynamics with tessellation techniques
NASA Astrophysics Data System (ADS)
Heß, Steffen; Springel, Volker
2010-08-01
Lagrangian smoothed particle hydrodynamics (SPH) is a well-established approach to model fluids in astrophysical problems, thanks to its geometric flexibility and ability to automatically adjust the spatial resolution to the clumping of matter. However, a number of recent studies have emphasized inaccuracies of SPH in the treatment of fluid instabilities. The origin of these numerical problems can be traced back to spurious surface effects across contact discontinuities, and to SPH's inherent prevention of mixing at the particle level. We here investigate a new fluid particle model where the density estimate is carried out with the help of an auxiliary mesh constructed as the Voronoi tessellation of the simulation particles instead of an adaptive smoothing kernel. This Voronoi-based approach improves the ability of the scheme to represent sharp contact discontinuities. We show that this eliminates spurious surface tension effects present in SPH and that play a role in suppressing certain fluid instabilities. We find that the new `Voronoi Particle Hydrodynamics' (VPH) described here produces comparable results to SPH in shocks, and better ones in turbulent regimes of pure hydrodynamical simulations. We also discuss formulations of the artificial viscosity needed in this scheme and how judiciously chosen correction forces can be derived in order to maintain a high degree of particle order and hence a regular Voronoi mesh. This is especially helpful in simulating self-gravitating fluids with existing gravity solvers used for N-body simulations.
Near-critical fluid hydrodynamics
NASA Astrophysics Data System (ADS)
Zappoli, Bernard
2003-10-01
In the vicinity of the gas-liquid critical point, transport coefficients of pure fluids experience important changes. In particular, the thermal diffusivity tends to zero whereas the isothermal compressibility tends to infinity. Supercritical fluids are thus as dense as liquids and much more expandable than gases. These properties make the hydrodynamic similarity parameters vary over orders of magnitude when nearing the critical point, thus leading to a large field of research. We review here four main fields: heat transfer, cavity flows, interfaces and hydrodynamic instabilities. In the first, we present a fourth adiabatic heat transfer mechanism, called the piston effect, which carries heat much faster than diffusion, in the absence of convection. In the second, we show how this heat transfer mechanism interacts with buoyant convection. In the third, we basically show that a thermally non-homogeneous near-critical fluid behaves as a two miscible-phases fluid. In the fourth, we present some specific behavior of the Rayleigh-Benard convection, as recent experiments and numerical simulations have indicated. The last part gives some pathways in the continuation of the current research. We stress the need to fully develop the hydrodynamic of highly expandable, low heat diffusing fluids since the subject is both a bearer of new physics and is needed for the development of processes in chemical engineering. To cite this article: B. Zappoli, C. R. Mecanique 331 (2003).
Some open questions in hydrodynamics
Mateusz Dyndal; Laurent Schoeffel
2014-12-16
When speaking of unsolved problems in physics, this is surprising at first glance to discuss the case of fluid mechanics. However, there are many deep open questions that come with the theory of fluid mechanics. In this paper, we discuss some of them that we classify in two categories, the long term behavior of solutions of equations of hydrodynamics and the definition of initial (boundary) conditions. The first set of questions come with the non-relativistic theory based on the Navier-Stokes equations. Starting from smooth initial conditions, the purpose is to understand if solutions of Navier-Stokes equations remain smooth with the time evolution. Existence for just a finite time would imply the evolution of finite time singularities, which would have a major influence on the development of turbulent phenomena. The second set of questions come with the relativistic theory of hydrodynamics. There is an accumulating evidence that this theory may be relevant for the description of the medium created in high energy heavy-ion collisions. However, this is not clear that the fundamental hypotheses of hydrodynamics are valid in this context. Also, the determination of initial conditions remains questionable. The purpose of this paper is to explore some ideas related to these questions, both in the non-relativistic and relativistic limits of fluid mechanics. We believe that these ideas do not concern only the theory side but can also be useful for interpreting results from experimental measurements.
Cluster Dynamics of Planetary Waves
Elena Kartashova; Victor S. L'vov
2008-11-05
The dynamics of nonlinear atmospheric planetary waves is determined by a small number of independent wave clusters consisting of a few connected resonant triads. We classified the different types of connections between neighboring triads that determine the general dynamics of a cluster. Each connection type corresponds to substantially different scenarios of energy flux among the modes. The general approach can be applied directly to various mesoscopic systems with 3-mode interactions, encountered in hydrodynamics, astronomy, plasma physics, chemistry, medicine, etc.
Stewart, Hannah Louise
and buoyancy in the tropical alga Turbinaria ornata Hannah L. Stewart* Department of Integrative Biology of buoyancy and flexural stiffness (EI) affect hydrodynamic forces on, and flow velocity relative by side on the reef at a site exposed to moderate wave action. To examine the effect of buoyancy alone
3212 Langmuir 1993,9,3212-3218 Hydrodynamic Modes of Viscoelastic Soap Films
Sens, Pierre
3212 Langmuir 1993,9,3212-3218 Hydrodynamic Modes of Viscoelastic Soap Films P. Sens,C. Marques of a soap f i i containing a viscoelastic Maxwellfluidmodelingawater solublepolymer. Twotypesof modesexist,bendingmodesand squeezing modes. In addition to the modes existing for a usual viscous soap f i i , we find Rayleigh waves
Jülicher, Frank
Flagellar Synchronization Independent of Hydrodynamic Interactions Benjamin M. Friedrich* and Frank of the flagellar pair of the green algae Chlamydomonas, we study theoretically a simple, mirror-symmetric swimmer waves [4]. Recently, the biflagellate green alga Chlamydomonas has emerged as an experimental model
HYDRODYNAMIC LIMITS FOR KINETIC EQUATIONS AND THE DIFFUSIVE APPROXIMATION OF RADIATIVE
HYDRODYNAMIC LIMITS FOR KINETIC EQUATIONS AND THE DIFFUSIVE APPROXIMATION OF RADIATIVE TRANSPORT FOR ACOUSTIC WAVES MANUEL PORTILHEIRO AND ATHANASIOS E. TZAVARAS Abstract. We consider a class of kinetic equation. The limits are obtained in the "dissipative" sense, equivalent to the notion of entropy solutions
Hydrodynamic modeling of tsunamis from the Currituck landslide
Geist, E.L.; Lynett, P.J.; Chaytor, J.D.
2009-01-01
Tsunami generation from the Currituck landslide offshore North Carolina and propagation of waves toward the U.S. coastline are modeled based on recent geotechnical analysis of slide movement. A long and intermediate wave modeling package (COULWAVE) based on the non-linear Boussinesq equations are used to simulate the tsunami. This model includes procedures to incorporate bottom friction, wave breaking, and overland flow during runup. Potential tsunamis generated from the Currituck landslide are analyzed using four approaches: (1) tsunami wave history is calculated from several different scenarios indicated by geotechnical stability and mobility analyses; (2) a sensitivity analysis is conducted to determine the effects of both landslide failure duration during generation and bottom friction along the continental shelf during propagation; (3) wave history is calculated over a regional area to determine the propagation of energy oblique to the slide axis; and (4) a high-resolution 1D model is developed to accurately model wave breaking and the combined influence of nonlinearity and dispersion during nearshore propagation and runup. The primary source parameter that affects tsunami severity for this case study is landslide volume, with failure duration having a secondary influence. Bottom friction during propagation across the continental shelf has a strong influence on the attenuation of the tsunami during propagation. The high-resolution 1D model also indicates that the tsunami undergoes nonlinear fission prior to wave breaking, generating independent, short-period waves. Wave breaking occurs approximately 40-50??km offshore where a tsunami bore is formed that persists during runup. These analyses illustrate the complex nature of landslide tsunamis, necessitating the use of detailed landslide stability/mobility models and higher-order hydrodynamic models to determine their hazard.
NASA Technical Reports Server (NTRS)
Lee, Jeongwoo W.
1993-01-01
In this paper we analyze the generation of waves in a sunspot by extending Stein's hydrodynamic approach to the turbulent medium permeated by a strong uniform magnetic field oriented parallel to the gravity. For wave sources appropriate to the sunspot, we consider magnetic perturbations and entropy changes as well as turbulent convection. To describe the anisotropy imposed by the sunspot, we use a one-dimensional correlation function relating the turbulent eddies separated along the symmetry axis of the spot. This treatment yields several interesting possibilities for wave generation in a sunspot. First, it is demonstrated that the entropy change and magnetic perturbation can lead to a relative enhancement of acoustic wave emission. Second, the energy flux of Alfven waves may be comparable to that of acoustic waves in sunspots. Third, the anisotropy of the sunspot dynamics can lead to wave energy spectrum in a form which may explain the origin of umbral atmospheric oscillations.
Vortex oscillations and hydrodynamics of rotating superfluids
NASA Astrophysics Data System (ADS)
Sonin, E. B.
1987-01-01
This review covers the progress in the study of vortex oscillations in rotating superfluids. The paper deals with the theory as its principal concern, but the experiments that one can compare with the theory considered are also discussed. Attention is focused mainly on the effects of crystalline order in the vortex lattice (the Tkachenko waves especially) and on the boundary problems arising in studies of vortex oscillations in finite containers. The approach is based mostly on the continuum hydrodynamic theory dealing with dense vortex arrays, and considerable attention is devoted to discussion of this theory in order to understand better the principles upon which the obtained results rest. The theory is traced from the simple description of a rotating classical fluid with continuous vorticity, through that of a perfect fluid with quantized vorticity in the form of an array of vortex lines, then the two-fluid theory of an isotropic superfluid, and finally the theory of rotating anisotropic superfluids such as 3He-A. Applications of the theory to He II, the superfluid phases of 3He, and the superfluid neutron matter in pulsars are discussed.
Hydrodynamic instability mechanism for rip currents
NASA Astrophysics Data System (ADS)
Yu, Jie
2015-04-01
On re-examining the hydrodynamic instability, Yu (J. Fluid Mech., vol. 549, 2006, pp. 403-428) showed that when the fully dynamical interactions are duly accounted for, and proper mathematical analysis is carried out, the positive feedback between the wave and evolving current can initiate and sustain rip current circulations with scales comparable to field observations on alongshore uniform beaches. In this study, we extend that analysis to consider non-planar beaches, and to include a new branch of unstable modes that correspond to alongshore propagating horizontal circulations with the magnitudes of the flow growing in time. This latter has not previously been studied. These propagating unstable modes have typical time periods of tens of minutes and alongshore propagation speeds of a few cm/sec. The physical implications of their spatial and slow time oscillations are discussed, as of relevance to occurrence and recurrence of transient rips, alongshore migration of rip currents and very low frequency pulsations in surf zone eddy circulations.
Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma
Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma I. Y. Dodin, V. I A hydrodynamic equation describing the linear evolution of a nondissipative Langmuir wave in inhomogeneous evolution varies depending on the wave geometry. © 2009 American Institute of Physics. doi:10
Hydrodynamics of internal solitons and a comparison of SIR-A and SIR-B data with ocean measurements
NASA Technical Reports Server (NTRS)
Apel, J. R.; Gasparovic, R. F.; Thompson, D. R.
1986-01-01
Large internal solitary waves have been observed by Shuttle SIR-A and SIR-B at locations in the Andaman Sea and the New York Bight. Satellite imagery and oceanographic measurements are used in conjunction with hydrodynamic interaction and electromagnetic scattering models to estimate the expected SAR image intensity modulations associated with the internal waves. There is reasonable agreement between the predicted and observed internal wave signatures.
Fasih Ramandi, Negin; Shemirani, Farzaneh
2015-10-15
Surfacted ferrofluid (S-FF) is a stable colloid dispersion of magnetic nanoparticles in a carrier liquid which possesses magnetic properties and fluidity simultaneously. Specifically in S-FF coating magnetic nanoparticles with a suitable surfactant provides steric repulsions to prevent particles agglomeration. Selecting the function of surfactant can be engineered according to its application. In the present study, for the first time the application of S-FF in dispersive solid phase extraction of methylene blue (as a cationic dye model) in water and shrimp samples was investigated. For this purpose, in order to use ionic liquid as carrier fluid, the surface of Fe3O4 nanoparticles was coated by an anionic surfactant in a polar medium to form a hydrophilic layer around magnetic nanoparticles. In addition to hydrophobic interactions between the analyte and carbonic chain of surfactant, the retention of cationic dye was mainly governed by attractive electrostatic interactions between polar head of surfactant and dye. Under optimized conditions, the relative standard deviation is 2.9%, the limit of detection is 2.5 ?g L(-1), and the preconcentration factor is 135. PMID:25952885
NASA Astrophysics Data System (ADS)
Nanjundappa, C. E.; Shivakumara, I. S.; Prakash, H. N.
2014-12-01
We investigate the influence of Coriolis force on the onset of thermomagnetic convection in ferrofluid saturating a porous layer in the presence of a uniform vertical magnetic field using both linear and weakly non-linear analyses. The modified Brinkman-Forchheimer-extended Darcy equation with Coriolis term has been used to describe the fluid flow. The linear theory based on normal mode method is considered to find the criteria for the onset of stationary thermomagnetic Convection and weakly non-linear analysis based on minimal representation of truncated Fourier series analysis containing only two terms has been used to find the Nusselt number Nu as functions of time. The range of thermal Rayleigh number R beyond which the bifurcation becomes subcritical increases with increasing ?, Da-1 and Ta. The global quantity of the heat transfer rate decreases by increasing the Taylor number Ta. The results obtained, during the above analyses, have been presented graphically and the effects of various parameters on heat and mass transfer have been discussed. Finally, we have drawn the steady streamlines for various parameters.
NASA Astrophysics Data System (ADS)
Mosher, Nathaniel; Perkins-Harbin, Emily; Aho, Brandon; Wang, Lihua; Kumon, Ronald; Rablau, Corneliu; Vaishnava, Prem; Tackett, Ronald; Therapeutic Biomaterials Group Team
2015-03-01
Colloidal suspensions of superparamagnetic nanoparticles, known as ferrofluids, are promising candidates for the mediation of magnetic fluid hyperthermia (MFH). In such materials, the dissipation of heat occurs as a result of the relaxation of the particles in an applied ac magnetic field via the Brownian and Neel mechanisms. In order to isolate and study the role of the Neel mechanism in this process, the sample can be frozen, using liquid nitrogen, in order to suppress the Brownian relaxation. In this experiment, dextran-coated Fe3O4 nanoparticles synthesized via co-precipitation and characterized via transmission electron microscopy and dc magnetization are used as MFH mediators over the temperature range between -70 °C to -10 °C (Brownian-suppressed state). Heating the nanoparticles using ac magnetic field (amplitude ~300 Oe), the frequency dependence of the specific absorption rate (SAR) is calculated between 150 kHz and 350 kHz and used to determine the magnetocrystalline anisotropy of the sample. We would like to thank Fluxtrol, Inc. for their help with this project
NASA Astrophysics Data System (ADS)
Hong, Ruo-Yu; Li, Jian-Hua; Zhang, Shi-Zhong; Li, Hong-Zhong; Zheng, Ying; Ding, Jian-min; Wei, Dong-Guang
2009-01-01
Fe 3O 4 magnetic nanoparticles (MNPs) were synthesized by the co-precipitation of Fe 3+ and Fe 2+ with ammonium hydroxide. The sodium citrate-modified Fe 3O 4 MNPs were prepared under Ar protection and were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). To improve the oxidation resistance of Fe 3O 4 MNPs, a silica layer was coated onto the modified and unmodified MNPs by the hydrolysis of tetraethoxysilane (TEOS) at 50 °C and pH 9. Afterwards, the silica-coated Fe 3O 4 core/shell MNPs were modified by oleic acid (OA) and were tested by IR and VSM. IR results revealed that the OA was successfully grafted onto the silica shell. The Fe 3O 4/SiO 2 core/shell MNPs modified by OA were used to prepare water-based ferrofluids (FFs) using PEG as the second layer of surfactants. The properties of FFs were characterized using a UV-vis spectrophotometer, a Gouy magnetic balance, a laser particle size analyzer and a Brookfield LVDV-III+ rheometer.
Constructing higher-order hydrodynamics: The third order
Grozdanov, Sašo
2015-01-01
Hydrodynamics can be formulated as the gradient expansion of conserved currents, in terms of the fundamental fields describing the near-equilibrium fluid flow. In the relativistic case, the Navier-Stokes equations follow from the conservation of the stress-energy tensor to first order in derivatives. In this paper, we go beyond the presently understood second-order hydrodynamics and discuss the systematisation of obtaining the hydrodynamic expansion to an arbitrarily high order. As an example, we fully classify the gradient expansion at third order for neutral fluids in four dimensions, thus finding the most general next-to-leading-order corrections to the relativistic Navier-Stokes equations. In the process, we list $20$ new transport coefficients in the conformal and $68$ in the non-conformal case. We also obtain the third-order corrections to the linear dispersion relations that describe the propagation of diffusion and sound waves in relativistic fluids. We apply our results to the energy-momentum transpo...
Constructing higher-order hydrodynamics: The third order
Sašo Grozdanov; Nikolaos Kaplis
2015-07-19
Hydrodynamics can be formulated as the gradient expansion of conserved currents in terms of the fundamental fields describing the near-equilibrium fluid flow. In the relativistic case, the Navier-Stokes equations follow from the conservation of the stress-energy tensor to first order in derivatives. In this paper, we go beyond the presently understood second-order hydrodynamics and discuss the systematisation of obtaining the hydrodynamic expansion to an arbitrarily high order. As an example of the algorithm that we present, we fully classify the gradient expansion at third order for neutral fluids in four dimensions, thus finding the most general next-to-leading-order corrections to the relativistic Navier-Stokes equations in curved space-time. In the process, we list $20$ new transport coefficients in the conformal and $68$ in the non-conformal case, without considering any constraints that could potentially arise from the entropy current analysis. We also obtain the third-order corrections to the linear dispersion relations that describe the propagation of diffusion and sound waves in relativistic fluids. We apply our results to the energy-momentum transport in the $\\mathcal{N}=4$ supersymmetric Yang-Mills fluid at infinite 't Hooft coupling and infinite number of colours, to find the values of two new conformal transport coefficients.
A hydrodynamic sensory antenna used by killifish for nocturnal hunting.
Schwarz, Jason S; Reichenbach, Tobias; Hudspeth, A J
2011-06-01
The perception of sensory stimuli by an animal requires several steps, commencing with the capture of stimulus energy by an antenna that, as the interface between the physical world and the nervous system, modifies the stimulus in ways that enhance the animal's perception. The mammalian external ear, for example, collects sound and spectrally alters it to increase sensitivity and improve the detection of directionality. In view of the morphological diversity of the lateral-line system across species and its accessibility to observation and experimental intervention, we sought to investigate the role of antennal structures on the response characteristics of the lateral line. The surface-feeding killifish Aplocheilus lineatus is able to hunt in darkness by detecting surface capillary waves with the lateral-line system atop its head. This cephalic lateral line consists of a stereotyped array of 18 mechanosensitive neuromasts bordered by fleshy ridges. By recording microphonic potentials, we found that each neuromast has a unique receptive field defined by its sensitivity to stimulation of the water's surface. The ridges help determine these receptive fields by altering the flow of water over each neuromast. Modification of the hydrodynamic environment by the addition of a supplemental ridge changes the pattern of water movement, perturbs the receptive fields of adjacent neuromasts and impairs the fish's localization ability. On the basis of electrophysiological, hydrodynamic and behavioral evidence, we propose that the ridges constitute a hydrodynamic antenna for the cephalic lateral line. PMID:21562172
Hydrodynamic Instability and Coalescence of Binary Neutron Stars
D. Lai; F. A. Rasio; S. L. Shapiro
1993-04-28
We study the importance of hydrodynamic effects on the evolution of coalescing binary neutron stars. Using an approximate energy functional constructed from equilibrium solutions for polytropic binary configurations, we incorporate hydrodynamic effects into the calculation of the orbital decay driven by gravitational wave emission. In particular, we follow the transition between the quasi-static, secular decay of the orbit at large separation and the rapid dynamical evolution of configurations approaching contact. We show that a purely Newtonian hydrodynamic instability can significantly accelerate the coalescence at small separation. Such an instability occurs in all close binary configurations containing sufficiently incompressible stars. Calculations are performed for various neutron star masses, radii, spins, and effective polytropic indices. Typically, we find that the radial infall velocity just prior to contact is about 10\\% of the tangential orbital velocity. Post-Newtonian effects can move the stability limit to a larger binary separation, and may induce an even larger radial velocity. We also consider the possibility of mass transfer from one neutron star to the other. We show that stable mass transfer is impossible except when the mass of one of the components is very small (less than about 0.4 solar mass) and the viscosity is high enough to maintain corotation.
Direct evidence of flagellar synchronization through hydrodynamic interactions
NASA Astrophysics Data System (ADS)
Brumley, Douglas; Polin, Marco; Wan, Kirsty; Goldstein, Raymond
2013-11-01
Eukaryotic cilia and flagella exhibit striking coordination, from the synchronous beating of two flagella in Chlamydomonas to the metachronal waves and large-scale flows displayed by carpets of cilia. However, the precise mechanisms responsible for flagellar synchronization remain unclear. We perform a series of experiments involving two individual flagella in a quiescent fluid. Cells are isolated from the colonial alga Volvox carteri, held in place at a fixed distance d, and oriented so that their flagellar beating planes coincide. In this fashion, we are able to explicitly assess the role of hydrodynamics in achieving synchronization. For closely separated cells, the flagella are capable of exhibiting a phase-locked state for thousands of beats at a time, despite significant differences in their intrinsic frequencies. For intermediate values of d, synchronous periods are interrupted by brief phase slips, while for d >> 1 the flagellar phase difference drifts almost linearly with time. The coupling strength extracted through analysis of the synchronization statistics exhibits excellent agreement with hydrodynamic predictions. This study unambiguously reveals that flagella coupled only through hydrodynamics are capable of exhibiting robust synchrony.
Denny, Mark
and animals that inhabit wave-swept environments are typically small compared with organisms that live hydrodynamic forces on exposed plants and animals, and wave-induced damage is characteristic of intertidal in either terrestrial habitats or marine habitats protected from waves. For example, the largest animals
Foundation of Hydrodynamics of Strongly Interacting Systems
Cheuk-Yin Wong
2014-04-03
Hydrodynamics and quantum mechanics have many elements in common, as the density field and velocity fields are common variables that can be constructed in both descriptions. Starting with the Schroedinger equation and the Klein-Gordon for a single particle in hydrodynamical form, we examine the basic assumptions under which a quantum system of particles interacting through their mean fields can be described by hydrodynamics.
Microscale hydrodynamics near moving contact lines
NASA Technical Reports Server (NTRS)
Garoff, Stephen; Chen, Q.; Rame, Enrique; Willson, K. R.
1994-01-01
The hydrodynamics governing the fluid motions on a microscopic scale near moving contact lines are different from those governing motion far from the contact line. We explore these unique hydrodynamics by detailed measurement of the shape of a fluid meniscus very close to a moving contact line. The validity of present models of the hydrodynamics near moving contact lines as well as the dynamic wetting characteristics of a family of polymer liquids are discussed.
Annual Report: Hydrodynamics and Radiative Hydrodynamics with Astrophysical Applications
R. Paul Drake
2005-12-01
We report the ongoing work of our group in hydrodynamics and radiative hydrodynamics with astrophysical applications. During the period of the existing grant, we have carried out two types of experiments at the Omega laser. One set of experiments has studied radiatively collapsing shocks, obtaining high-quality scaling data using a backlit pinhole and obtaining the first (ever, anywhere) Thomson-scattering data from a radiative shock. Other experiments have studied the deeply nonlinear development of the Rayleigh-Taylor (RT) instability from complex initial conditions, obtaining the first (ever, anywhere) dual-axis radiographic data using backlit pinholes and ungated detectors. All these experiments have applications to astrophysics, discussed in the corresponding papers either in print or in preparation. We also have obtained preliminary radiographs of experimental targets using our x-ray source. The targets for the experiments have been assembled at Michigan, where we also prepare many of the simple components. The above activities, in addition to a variety of data analysis and design projects, provide good experience for graduate and undergraduates students. In the process of doing this research we have built a research group that uses such work to train junior scientists.
Hydrodynamics of post CHF region
Ishii, M.; De Jarlais, G.
1984-04-01
Among various two-phase flow regimes, the inverted flow in the post-dryout region is relatively less well understood due to its special heat transfer conditions. The review of existing data indicates further research is needed in the areas of basic hydrodynamics related to liquid core disintegration mechanisms, slug and droplet formations, entrainment, and droplet size distributions. In view of this, the inverted flow is studied in detail both analytically and experimentally. Criteria for initial flow regimes in the post-dryout region are given. Preliminary models for subsequent flow regime transition criteria are derived together with correlations for a mean droplet diameter based on the adiabatic simulation data.
Disruptive Innovation in Numerical Hydrodynamics
Waltz, Jacob I.
2012-09-06
We propose the research and development of a high-fidelity hydrodynamic algorithm for tetrahedral meshes that will lead to a disruptive innovation in the numerical modeling of Laboratory problems. Our proposed innovation has the potential to reduce turnaround time by orders of magnitude relative to Advanced Simulation and Computing (ASC) codes; reduce simulation setup costs by millions of dollars per year; and effectively leverage Graphics Processing Unit (GPU) and future Exascale computing hardware. If successful, this work will lead to a dramatic leap forward in the Laboratory's quest for a predictive simulation capability.
Problems in astrophysical radiation hydrodynamics
Castor, J.I.
1983-09-14
The basic equations of radiation hydrodynamics are discussed in the regime that the radiation is dynamically as well as thermally important. Particular attention is paid to the question of what constitutes an acceptable approximate non-relativistic system of dynamical equations for matter and radiation in this regime. Further discussion is devoted to two classes of application of these ideas. The first class consists of problems dominated by line radiation, which is sensitive to the velocity field through the Doppler effect. The second class is of problems in which the advection of radiation by moving matter dominates radiation diffusion.
Minimal Model for Hydrodynamic Synchronization
Bian Qian; Hongyuan Jiang; David A. Gagnon; Kenneth S. Breuer; Thomas R. Powers
2009-12-05
Motivated by the observed coordination of nearby beating cilia, we use a scale model experiment to show that hydrodynamic interactions can cause synchronization between rotating paddles driven at constant torque in a very viscous fluid. Synchronization is only observed when the shafts supporting the paddles have some flexibility. The phase difference in the synchronized state depends on the symmetry of the paddles. We use the method of regularized stokeslets to model the paddles and find excellent agreement with the experimental observations. We also use a simple analytic theory based on far-field approximations to derive scaling laws for the synchronization time as a function of paddle separation.
Collision-dominated nonlinear hydrodynamics in graphene
Briscot, U; Gornyi, I V; Titov, M; Narozhny, B N; Mirlin, A D
2015-01-01
We present an effective hydrodynamic theory of electronic transport in graphene in the interaction-dominated regime. We derive the emergent hydrodynamic description from the microscopic Boltzmann kinetic equation taking into account dissipation due to Coulomb interaction and find the viscosity of Dirac fermions in graphene for arbitrary densities. The viscous terms have a dramatic effect on transport coefficients in clean samples at high temperatures. Within linear response, we show that viscosity manifests itself in the nonlocal conductivity as well as dispersion of hydrodynamic plasmons. Beyond linear response, we apply the derived nonlinear hydrodynamics to the problem of hot spot relaxation in graphene.
Hydrodynamic interactions in active colloidal crystal microrheology.
Weeber, R; Harting, J
2012-11-01
In dense colloids it is commonly assumed that hydrodynamic interactions do not play a role. However, a found theoretical quantification is often missing. We present computer simulations that are motivated by experiments where a large colloidal particle is dragged through a colloidal crystal. To qualify the influence of long-ranged hydrodynamics, we model the setup by conventional Langevin dynamics simulations and by an improved scheme with limited hydrodynamic interactions. This scheme significantly improves our results and allows to show that hydrodynamics strongly impacts the development of defects, the crystal regeneration, as well as the jamming behavior. PMID:23214913
Hydrodynamic interactions in active colloidal crystal microrheology
Rudolf Weeber; Jens Harting
2012-10-26
In dense colloids it is commonly assumed that hydrodynamic interactions do not play a role. However, a found theoretical quantification is often missing. We present computer simulations that are motivated by experiments where a large colloidal particle is dragged through a colloidal crystal. To qualify the influence of long-ranged hydrodynamics, we model the setup by conventional Langevin dynamics simulations and by an improved scheme with limited hydrodynamic interactions. This scheme significantly improves our results and allows to show that hydrodynamics strongly impacts on the development of defects, the crystal regeneration as well as on the jamming behavior.
Kristofikova, Zdena; Gazova, Zuzana; Siposova, Katarina; Bartos, Ales; Ricny, Jan; Kotoucova, Jolana; Sirova, Jana; Ripova, Daniela
2014-08-01
It is well known that misfolded peptides/proteins can play a role in processes of normal ageing and in the pathogenesis of many diseases including Alzheimer's disease. Previously, we evaluated samples of cerebrospinal fluid from patients with Alzheimer's disease and multiple sclerosis by means of thioflavin-T-based fluorescence. We observed attenuated effects of magnetite nanoparticles operated via anti-aggregation actions on peptides/proteins from patients with Alzheimer's disease but not from those with multiple sclerosis when compared to age-related controls. In this study, we have evaluated the in vitro effects of anti-aggregation operating ferrofluid and phytoalexin spirobrassinin in the cerebrospinal fluid of patients with multiple sclerosis and Alzheimer's disease. We have found significant differences in native fluorescence (? excitation = 440 nm, ? emission = 485 nm) of samples among particular groups (young controls < multiple sclerosis, Alzheimer's disease < old controls). Differences among groups were observed also in thioflavin-T-based fluorescence (young controls = multiple sclerosis < Alzheimer's disease < old controls) and the most marked change from native to thioflavin-T-based fluorescence was found in young controls (28-40 years old people). Both ferrofluid and spirobrassinin evoked drops in thioflavin-T-based fluorescence; however, ferrofluid was more efficient in old controls (54-75 years old people) and spirobrassinin in multiple sclerosis patients, both compared to young controls. The results are discussed especially in relation to aggregated peptides/proteins and liposoluble fluorescent products of lipid peroxidation. Based on the significant effect of spirobrassinin in vitro, we suggest that spirobrassinin may be of therapeutic value in multiple sclerosis. PMID:24858241
Effects of Second-Order Hydrodynamics on a Semisubmersible Floating Offshore Wind Turbine: Preprint
Bayati, I.; Jonkman, J.; Robertson, A.; Platt, A.
2014-07-01
The objective of this paper is to assess the second-order hydrodynamic effects on a semisubmersible floating offshore wind turbine. Second-order hydrodynamics induce loads and motions at the sum- and difference-frequencies of the incident waves. These effects have often been ignored in offshore wind analysis, under the assumption that they are significantly smaller than first-order effects. The sum- and difference-frequency loads can, however, excite eigenfrequencies of the system, leading to large oscillations that strain the mooring system or vibrations that cause fatigue damage to the structure. Observations of supposed second-order responses in wave-tank tests performed by the DeepCwind consortium at the MARIN offshore basin suggest that these effects might be more important than originally expected. These observations inspired interest in investigating how second-order excitation affects floating offshore wind turbines and whether second-order hydrodynamics should be included in offshore wind simulation tools like FAST in the future. In this work, the effects of second-order hydrodynamics on a floating semisubmersible offshore wind turbine are investigated. Because FAST is currently unable to account for second-order effects, a method to assess these effects was applied in which linearized properties of the floating wind system derived from FAST (including the 6x6 mass and stiffness matrices) are used by WAMIT to solve the first- and second-order hydrodynamics problems in the frequency domain. The method has been applied to the OC4-DeepCwind semisubmersible platform, supporting the NREL 5-MW baseline wind turbine. The loads and response of the system due to the second-order hydrodynamics are analysed and compared to first-order hydrodynamic loads and induced motions in the frequency domain. Further, the second-order loads and induced response data are compared to the loads and motions induced by aerodynamic loading as solved by FAST.
The effects of second-order hydrodynamics on a semisubmersible floating offshore wind turbine
NASA Astrophysics Data System (ADS)
Bayati, I.; Jonkman, J.; Robertson, A.; Platt, A.
2014-06-01
The objective of this paper is to assess the second-order hydrodynamic effects on a semisubmersible floating offshore wind turbine. Second-order hydrodynamics induce loads and motions at the sum- and difference-frequencies of the incident waves. These effects have often been ignored in offshore wind analysis, under the assumption that they are significantly smaller than first-order effects. The sum- and difference-frequency loads can, however, excite eigenfrequencies of a floating system, leading to large oscillations that strain the mooring system or vibrations that cause fatigue damage to the structure. Observations of supposed second-order responses in wave-tank tests performed by the DeepCwind consortium at the Maritime Research Institute Netherlands (MARIN) offshore basin suggest that these effects might be more important than originally expected. These observations inspired interest in investigating how second-order excitation affects floating offshore wind turbines and whether second-order hydrodynamics should be included in offshore wind simulation tools like FAST. In this work, the effects of second-order hydrodynamics on a floating semisubmersible offshore wind turbine are investigated. Because FAST is currently unable to account for second-order effects, a method to assess these effects was applied in which linearized properties of the floating wind system derived from FAST (including the 6x6 mass and stiffness matrices) are used by WAMIT to solve the first- and second-order hydrodynamics problems in the frequency domain. The method was applied to the Offshore Code Comparison Collaboration Continuation OC4-DeepCwind semisubmersible platform, supporting the National Renewable Energy Laboratory's 5-MW baseline wind turbine. In this paper, the loads and response of the system caused by the second-order hydrodynamics are analysed and compared to the first-order hydrodynamic loads and induced motions in the frequency domain. Further, the second-order loads and induced response data are compared to the loads and motions induced by aerodynamic loading as solved by FAST.
Hydrodynamic Instability of Liquid Films on Moving Fibers.
Kornev; Neimark
1999-07-15
The stability of liquid films on moving fibers is studied with a focus on effects caused by film-solid adhesion interactions and hydrodynamic interactions between the film and the surrounding gas. We show that at high fiber velocities (large Reynolds numbers) the film-gas hydrodynamic interactions induce instability in films, which would, otherwise, be stabilized by the adhesion interactions at static conditions. Two types of unstable modes caused by hydrodynamic factors are found: the first corresponds to the Kelvin-Helmholtz waves induced by inertia effects; the second, induced by viscosity effects, is observed at smaller (yet still large) Reynolds numbers when the Kelvin-Helmholtz instability is suppressed. Linear stability analysis of the system of coupled hydrodynamic equations of film and gas flow is performed by the method of normal modes. We derive the general dispersion relation as an implicit equation with respect to the mode frequency. In the limit of vanishing fiber velocities, the obtained equation provides the dispersion equation for motionless fibers. The conditions of film stability and unstable modes are analyzed in terms of two dimensionless parameters, the adhesion factor, which quantifies the intensity of film-fiber interactions, and the Weber number, which quantifies the intensity of film-gas interactions. The Reynolds number determines the regions of validity of the inviscid and viscous regimes of film instability. The results are illustrated by estimates of the stability conditions for moving fibers in terms of the stability diagram, the critical film thickness, the fastest unstable mode, and the corresponding characteristic break-up time. Although the methods developed are applicable for any type of liquid-solid interaction, the estimates were made for the long-range van der Waals interactions. Practical applications include various technologies related to fabrication and chemical modifications of fibers and fiber products, e.g., spin finishing and lubrication. Copyright 1999 Academic Press. PMID:10419674
Delphine El Kharrat; Olivier Sandre; Régine Perzynski; Frédéric Chécot; Sébastien Lecommandoux
2007-09-21
A novel type of hybrid colloids is presented, based on the association of several polymeric systems and ferrofluids. On the one hand, we use inorganic nanoparticles made of magnetic iron oxide prepared at the LI2C, which response to a magnetic field of low intensity. On the other hand the organic part is made either of long linear polyacrylamide chains or of mesoscopic structures (vesicles and micelles) self-assembled from amphiphile polybutadiene-b-poly(glutamic acid) di-block copolymers, which conformation is pH-sensitive.
NASA Astrophysics Data System (ADS)
Liao, Shu-Hsien; Liu, Chieh-Wen; Yang, Hong-Chang; Chen, Hsin-Hsien; Chen, Ming-Jye; Chen, Kuen-Lin; Horng, Herng-Er; Wang, Li-Min; Yang, Shieh-Yueh
2012-06-01
In this work, the spin-spin relaxation of protons in ferrofluids is characterized using a high-Tc SQUID-based detector in microtesla fields. We found that spin-spin relaxation rate is enhanced in the presence of superparamagnetic nanoparticles. The enhanced relaxation rates are attributed to the microscopic field gradients from magnetic nanoparticles that dephase protons' spins nearby. The relaxation rates decrease when temperatures increase. Additionally, the alternating current magnetic susceptibility was inversely proportional to temperature. Those characteristics explained the enhanced Brownian motion of nanoparticles at high temperatures. Characterizing the relaxation will be helpful for assaying bio-molecules and magnetic resonance imaging in microtesla fields.
Hydrodynamic force characteristics of slender cylinders in the splash zone
Haritos, N.; Daliri, M.R.
1995-12-31
This paper presents results from a pilot experimental program of research being performed on segmented vertical surface-piercing cylinders in the Department of Civil and Environmental Engineering at The University of Melbourne. The primary aim of this investigation is to determine the influence of the splash zone on the hydrodynamic force characteristics of such cylinders to wave loading in the Morison regime. This influence is assessed from a comparison of the observed force characteristics of instrumented segments located in the splash zone with the corresponding results obtained from similarly instrumented segments located in the fully submerged zone and from those obtained for the cylinder as a whole via measurements of the cylinder tip restraint force. Results to hand for uni-directional regular waves suggest that there appears to be a mild frequency dependence in the inertia force coefficient in the splash zone which only marginally exceeds the corresponding values observed for a submerged segment immediately below this zone.
Raphael, Elie
Capillary-gravity waves on depth-dependent currents: Consequences for the wave resistance.1209/0295-5075/97/14007 Capillary-gravity waves on depth-dependent currents: Consequences for the wave resistance M. Benzaquen and E.35.-i Hydrodynamic waves PACS 68.03.-g Gas-liquid and vacuum-liquid interfaces Abstract We study
Mirror-type Boundary Condition in Smoothed Particle Hydrodynamics
NASA Astrophysics Data System (ADS)
Marjani, A.; Edge, B. L.
2013-12-01
The main purpose of this study is to enhance the Smoothed Particle Hydrodynamics (SPH) method that can accurately simulate the hydrodynamic forces on a structure and can be used for determining efficient designs for wave energy devices. Smoothed particle hydrodynamics is a method used in various fields of study. Unlike the finite difference method (FDM), SPH is a Lagrangian mesh-free method in which each particle moves according to the property of the surrounding flow and governing conservation equations, and carries the properties of water such as density, pressure and mass. Smoothed Particle Hydrodynamics is recently applied to a wide range of fluid mechanics problems. Although it is known as a highly accurate model, slow performance in 3D interface is one of its drawbacks. Not only the computational time becomes very long but also the number of processors and required memory are not easily available. Practical applications deal with high Reynolds numbers that requires high resolution to achieve adequate accuracy. A large number of coastal engineering problems are geometrically symmetric; hence, as a solution, mirror boundary condition is introduced and applied to two different tests in this paper, one is the impact of solitary wave on a large circular cylinder and the other is the interaction of dam break wave and structure. Mirror boundary condition can either produce a remarkable speedup with the same number of processors or the same running time with less number of processors. Regarding the fact that SPH algorithm yields Np log(Np) particle interactions at each time step, reducing the number of particles by a factor of 2 decreases the total number of interactions by a factor greater than 2. In other words, the relation between computational time and the number of particles does not behave like a linear function. Results show that smaller number of particles results in fewer particle interactions and less communications between processors. We believe that this technique is one of the best approaches to reduce the total number of particles by half. Simulating the half-basin model leads to a significant speedup of about 2.7. Half-basin model reproduces the laboratory data as precisely as full-size model does. Dam Break test by SPH - Half basin
Active and driven hydrodynamic crystals
Nicolas Desreumaux; Nicolas Florent; Eric Lauga; Denis Bartolo
2012-09-05
Motivated by the experimental ability to produce monodisperse particles in microfluidic devices, we study theoretically the hydrodynamic stability of driven and active crystals. We first recall the theoretical tools allowing to quantify the dynamics of elongated particles in a confined fluid. In this regime hydrodynamic interactions between particles arise from a superposition of potential dipolar singularities. We exploit this feature to derive the equations of motion for the particle positions and orientations. After showing that all five planar Bravais lattices are stationary solutions of the equations of motion, we consider separately the case where the particles are passively driven by an external force, and the situation where they are self-propelling. We first demonstrate that phonon modes propagate in driven crystals, which are always marginally stable. The spatial structure of the eigenmodes depend solely on the symmetries of the lattices, and on the orientation of the driving force. For active crystals, the stability of the particle positions and orientations depends not only on the symmetry of the crystals but also on the perturbation wavelengths and on the crystal density. Unlike unconfined fluids, the stability of active crystals is independent of the nature of the propulsion mechanism at the single particle level. The square and rectangular lattices are found to be linearly unstable at short wavelengths provided the volume fraction of the crystals is high enough. Differently, hexagonal, oblique, and face-centered crystals are always unstable. Our work provides a theoretical basis for future experimental work on flowing microfluidic crystals.
Hydrodynamic dispersion within porous biofilms
NASA Astrophysics Data System (ADS)
Davit, Y.; Byrne, H.; Osborne, J.; Pitt-Francis, J.; Gavaghan, D.; Quintard, M.
2013-01-01
Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher's equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels' network; (2) the solute's diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport.
Some open questions in hydrodynamics
Dyndal, Mateusz
2014-01-01
When speaking of unsolved problems in physics, this is surprising at first glance to discuss the case of fluid mechanics. However, there are many deep open questions that come with the theory of fluid mechanics. In this paper, we discuss some of them that we classify in two categories, the long term behavior of solutions of equations of hydrodynamics and the definition of initial (boundary) conditions. The first set of questions come with the non-relativistic theory based on the Navier-Stokes equations. Starting from smooth initial conditions, the purpose is to understand if solutions of Navier-Stokes equations remain smooth with the time evolution. Existence for just a finite time would imply the evolution of finite time singularities, which would have a major influence on the development of turbulent phenomena. The second set of questions come with the relativistic theory of hydrodynamics. There is an accumulating evidence that this theory may be relevant for the description of the medium created in high en...
Hydrodynamic Flow from Fast Particles
Casalderrey-Solana, J; Teaney, D
2006-01-01
We study the interaction of a fast moving particle in the Quark Gluon Plasma with linearized hydrodynamics. We derive the linearized hydrodynamic equations on top of an expanding fireball, and detail the solutions for a static medium. There are two modes far from the jet -- a sound mode and a diffusion mode. The diffusion mode is localized in a narrow wake behind the jet while the sound mode propagates at the Mach angle, $\\cos(\\theta_M) = c_s/c$. A general argument shows that the strength of the diffusion mode relative to the sound mode is directly proportional to the entropy produced by the jet-medium interaction. This argument does not rely on the linearized approximation and the assumption of local thermal equilibrium close to the jet. With this insight we calculate the spectrum of secondaries associated with the fast moving particle. If the energy loss is large and the jet-medium interaction does not produce significant entropy, the flow at the Mach angle can be observed in the associated spectrum. Howeve...
Two dimensional hydrodynamic modeling of a high latitude braided river
NASA Astrophysics Data System (ADS)
Humphries, E.; Pavelsky, T.; Bates, P. D.
2014-12-01
Rivers are a fundamental resource to physical, ecologic and human systems, yet quantification of river flow in high-latitude environments remains limited due to the prevalence of complex morphologies, remote locations and sparse in situ monitoring equipment. Advances in hydrodynamic modeling and remote sensing technology allow us to address questions such as: How well can two-dimensional models simulate a flood wave in a highly 3-dimensional braided river environment, and how does the structure of such a flood wave differ from flow down a similar-sized single-channel river? Here, we use the raster-based hydrodynamic model LISFLOOD-FP to simulate flood waves, discharge, water surface height, and velocity measurements over a ~70 km reach of the Tanana River in Alaska. In order to use LISFLOOD-FP a digital elevation model (DEM) fused with detailed bathymetric data is required. During summer 2013, we surveyed 220,000 bathymetric points along the study reach using an echo sounder system connected to a high-precision GPS unit. The measurements are interpolated to a smooth bathymetric surface, using Topo to Raster interpolation, and combined with an existing five meter DEM (Alaska IfSAR) to create a seamless river terrain model. Flood waves are simulated using varying complexities in model solvers, then compared to gauge records and water logger data to assess major sources of model uncertainty. Velocity and flow direction maps are also assessed and quantified for detailed analysis of braided channel flow. The most accurate model output occurs with using the full two-dimensional model structure, and major inaccuracies appear to be related to DEM quality and roughness values. Future work will intercompare model outputs with extensive ground measurements and new data from AirSWOT, an airborne analog for the Surface Water and Ocean Topography (SWOT) mission, which aims to provide high-resolution measurements of terrestrial and ocean water surface elevations globally.
Reliable estimation of shock position in shock-capturing compressible hydrodynamics codes
Nelson, Eric M
2008-01-01
The displacement method for estimating shock position in a shock-capturing compressible hydrodynamics code is introduced. Common estimates use simulation data within the captured shock, but the displacement method uses data behind the shock, making the estimate consistent with and as reliable as estimates of material parameters obtained from averages or fits behind the shock. The displacement method is described in the context of a steady shock in a one-dimensional lagrangian hydrodynamics code, and demonstrated on a piston problem and a spherical blast wave.The displacement method's estimates of shock position are much better than common estimates in such applications.
NASA Astrophysics Data System (ADS)
Belyakov, Vladimir; Makarov, Vladimir; Zezyulin, Denis; Kurkin, Andrey; Pelinovsky, Efim
2015-04-01
Hazardous phenomena in the coastal zone lead to the topographic changing which are difficulty inspected by traditional methods. It is why those autonomous robots are used for collection of nearshore topographic and hydrodynamic measurements. The robot RTS-Hanna is well-known (Wubbold, F., Hentschel, M., Vousdoukas, M., and Wagner, B. Application of an autonomous robot for the collection of nearshore topographic and hydrodynamic measurements. Coastal Engineering Proceedings, 2012, vol. 33, Paper 53). We describe here several constructions of mobile systems developed in Laboratory "Transported Machines and Transported Complexes", Nizhny Novgorod State Technical University. They can be used in the field surveys and monitoring of wave regimes nearshore.
Integrable GL(2) Geometry and Hydrodynamic Partial Differential Equations
Smith, Abraham D
2009-01-01
This article is a local analysis of integrable GL(2)-structures of degree 4. A GL(2)-structure of degree $n$ corresponds to a distribution of rational normal cones over a manifold M of dimension ${n+1}$. Integrability corresponds to the existence of many submanifolds that are spanned by lines in the cones. These GL(2)-structures are important because they naturally arise from a certain family of second-order hyperbolic PDEs in three variables that are integrable via hydrodynamic reduction. Familiar examples include the wave equation, the first flow of the dKP equation, and the Boyer--Finley equation. The main results are a structure theorem for integrable GL(2)-structures, a classification for connected integrable GL(2)-structures, and an equivalence between local integrable GL(2)-structures and Hessian hydrodynamic hyperbolic PDEs in three variables. This yields natural geometric characterizations of the wave equation, the first flow of the dKP equation, and several others. It also provides an intrinsic, coo...
NSDL National Science Digital Library
2014-09-18
Students learn about the types of waves and how they change direction, as well as basic wave properties such as wavelength, frequency, amplitude and speed. During the presentation of lecture information on wave characteristics and properties, students take notes using a handout. Then they label wave parts on a worksheet diagram and draw their own waves with specified properties (crest, trough and wavelength). They also make observations about the waves they drew to determine which has the highest and the lowest frequency. With this knowledge, students better understand waves and are a step closer to understanding how humans see color.
Cycloidal Wave Energy Converter
Stefan G. Siegel, Ph.D.
2012-11-30
This program allowed further advancing the development of a novel type of wave energy converter, a Cycloidal Wave Energy Converter or CycWEC. A CycWEC consists of one or more hydrofoils rotating around a central shaft, and operates fully submerged beneath the water surface. It operates under feedback control sensing the incoming waves, and converts wave power to shaft power directly without any intermediate power take off system. Previous research consisting of numerical simulations and two dimensional small 1:300 scale wave flume experiments had indicated wave cancellation efficiencies beyond 95%. The present work was centered on construction and testing of a 1:10 scale model and conducting two testing campaigns in a three dimensional wave basin. These experiments allowed for the first time for direct measurement of electrical power generated as well as the interaction of the CycWEC in a three dimensional environment. The Atargis team successfully conducted two testing campaigns at the Texas A&M Offshore Technology Research Center and was able to demonstrate electricity generation. In addition, three dimensional wave diffraction results show the ability to achieve wave focusing, thus increasing the amount of wave power that can be extracted beyond what was expected from earlier two dimensional investigations. Numerical results showed wave cancellation efficiencies for irregular waves to be on par with results for regular waves over a wide range of wave lengths. Using the results from previous simulations and experiments a full scale prototype was designed and its performance in a North Atlantic wave climate of average 30kW/m of wave crest was estimated. A full scale WEC with a blade span of 150m will deliver a design power of 5MW at an estimated levelized cost of energy (LCOE) in the range of 10-17 US cents per kWh. Based on the new results achieved in the 1:10 scale experiments these estimates appear conservative and the likely performance at full scale will exceed this initial performance estimates. In advancing the Technology Readiness Level (TRL) of this type of wave energy converter from 3 to 4, we find the CycWEC to exceed our initial estimates in terms of hydrodynamic performance. Once fully developed and optimized, it has the potential to not just outperform all other WEC technologies, but to also deliver power at a lower LCOE than competing conventional renewables like wind and solar. Given the large wave power resource both domestically and internationally, this technology has the potential to lead to a large improvement in our ability to produce clean electricity at affordable cost.
Hydrodynamic effects in driven soft matter
Manoel Manghi; Xaver Schlagberger; Yong-Woon Kim; Roland R. Netz
2012-03-07
Recent theoretical works exploring the hydrodynamics of soft material in non-equilibrium situations are reviewed. We discuss the role of hydrodynamic interactions for three different systems: i) the deformation and orientation of sedimenting semiflexible polymers, ii) the propulsion and force-rectification with a nano-machine realized by a rotating elastic rod, and iii) the deformation of a brush made of grafted semiflexible polymers in shear flows. In all these examples deformable polymers are subject to various hydrodynamic flows and hydrodynamic interactions. Perfect stiff nano-cylinders are known to show no orientational effects as they sediment through a viscous fluid, but it is the coupling between elasticity and hydrodynamic torques that leads to an orientation perpendicular to the direction of sedimentation. Likewise, a rotating stiff rod does not lead to a net propulsion in the Stokes limit, but if bending is allowed an effective thrust develops whose strength and direction is independent of the sense of rotation and thus acts as a rectification device. Lastly, surface-anchored polymers are deformed by shear flows, which modifies the effective hydrodynamic boundary condition in a non-linear fashion. All these results are obtained with hydrodynamic Brownian dynamics simulation techniques, as appropriate for dilute systems. Scaling analyses are presented when possible. The common theme is the interaction between elasticity of soft matter and hydrodynamics, which can lead to qualitatively new effects.
Relativistic Hydrodynamics for Heavy-Ion Collisions
ERIC Educational Resources Information Center
Ollitrault, Jean-Yves
2008-01-01
Relativistic hydrodynamics is essential to our current understanding of nucleus-nucleus collisions at ultrarelativistic energies (current experiments at the Relativistic Heavy Ion Collider, forthcoming experiments at the CERN Large Hadron Collider). This is an introduction to relativistic hydrodynamics for graduate students. It includes a detailed…
Hydrodynamic models of a Cepheid atmosphere
NASA Technical Reports Server (NTRS)
Karp, A. H.
1975-01-01
Instead of computing a large number of coarsely zoned hydrodynamic models covering the entire atmospheric instability strip, the author computed a single model as well as computer limitations allow. The implicit hydrodynamic code of Kutter and Sparks was modified to include radiative transfer effects in optically thin zones.
Direct Surface Extraction from Smoothed Particle Hydrodynamics
Linsen, Lars
Direct Surface Extraction from Smoothed Particle Hydrodynamics Simulation Data Paul Rosenthal1. To visualize the simulated particle data at a certain point in time, we propose a method that extracts surfaces a method that directly extracts surfaces from smoothed par- ticle hydrodynamics simulation data without 3D
Extended Hydrodynamical Model of Carrier Transport in Semiconductors
Russo, Giovanni
Extended Hydrodynamical Model of Carrier Transport in Semiconductors Angelo Marcello Anile \\Lambda title: Extended Hydrodynamical Model in Semiconductors Abstract A hydrodynamical model based on the theory of Extended ThermoÂ dynamics is presented for carrier transport in semiconductors. Closure
Smoothed Particle Hydrodynamics in Flood Simulations Michal Chladek
Durikovic, Roman
Smoothed Particle Hydrodynamics in Flood Simulations Michal Chl´adek Comenius University fluid simulation. Namely smoothed particle hydrodynamics (SPH) [Monaghan 1992] and MPS [Koshizuka Smoothed particle hydrodynamics is a Lagrangian fluid simulation method originally developed for simulating
Hydrodynamics, Fungal Physiology, and Morphology.
Serrano-Carreón, L; Galindo, E; Rocha-Valadéz, J A; Holguín-Salas, A; Corkidi, G
2015-01-01
Filamentous cultures, such as fungi and actinomycetes, contribute substantially to the pharmaceutical industry and to enzyme production, with an annual market of about 6 billion dollars. In mechanically stirred reactors, most frequently used in fermentation industry, microbial growth and metabolite productivity depend on complex interactions between hydrodynamics, oxygen transfer, and mycelial morphology. The dissipation of energy through mechanically stirring devices, either flasks or tanks, impacts both microbial growth through shearing forces on the cells and the transfer of mass and energy, improving the contact between phases (i.e., air bubbles and microorganisms) but also causing damage to the cells at high energy dissipation rates. Mechanical-induced signaling in the cells triggers the molecular responses to shear stress; however, the complete mechanism is not known. Volumetric power input and, more importantly, the energy dissipation/circulation function are the main parameters determining mycelial size, a phenomenon that can be explained by the interaction of mycelial aggregates and Kolmogorov eddies. The use of microparticles in fungal cultures is also a strategy to increase process productivity and reproducibility by controlling fungal morphology. In order to rigorously study the effects of hydrodynamics on the physiology of fungal microorganisms, it is necessary to rule out the possible associated effects of dissolved oxygen, something which has been reported scarcely. At the other hand, the processes of phase dispersion (including the suspended solid that is the filamentous biomass) are crucial in order to get an integral knowledge about biological and physicochemical interactions within the bioreactor. Digital image analysis is a powerful tool for getting relevant information in order to establish the mechanisms of mass transfer as well as to evaluate the viability of the mycelia. This review focuses on (a) the main characteristics of the two most common morphologies exhibited by filamentous microorganisms; (b) how hydrodynamic conditions affect morphology and physiology in filamentous cultures; and (c) techniques using digital image analysis to characterize the viability of filamentous microorganisms and mass transfer in multiphase dispersions. Representative case studies of fungi (Trichoderma harzianum and Pleurotus ostreatus) exhibiting different typical morphologies (disperse mycelia and pellets) are discussed. PMID:25652005
Effect of Surface Roughness on Hydrodynamic Bearings
NASA Technical Reports Server (NTRS)
Majumdar, B. C.; Hamrock, B. J.
1981-01-01
A theoretical analysis on the performance of hydrodynamic oil bearings is made considering surface roughness effect. The hydrodynamic as well as asperity contact load is found. The contact pressure was calculated with the assumption that the surface height distribution was Gaussian. The average Reynolds equation of partially lubricated surface was used to calculate hydrodynamic load. An analytical expression for average gap was found and was introduced to modify the average Reynolds equation. The resulting boundary value problem was then solved numerically by finite difference methods using the method of successive over relaxation. The pressure distribution and hydrodynamic load capacity of plane slider and journal bearings were calculated for various design data. The effects of attitude and roughness of surface on the bearing performance were shown. The results are compared with similar available solution of rough surface bearings. It is shown that: (1) the contribution of contact load is not significant; and (2) the hydrodynamic and contact load increase with surface roughness.
Analogies and distinctions between hydrodynamic and optical nonlinear waves
NASA Astrophysics Data System (ADS)
Mena-Contla, A.; Peña-Moreno, R.; Morales-Lara, L.; Serkin, V. N.; Belyaeva, T. L.
2015-01-01
We present the algorithm based on the Lax pair generalization to reveal some properties of nonautonomous KdV solitons. Starting from the general method of solution for the nonisospectral IST problem, we demonstrate how the varying-coefficient KdV equation can arise in nonuniformed and inhomogeneous media. We write down the one- and two-soliton solution of the nonautonomous varying-coefficient KdV with the time-dependent spectral parameter and consider some special cases of the isospectral solutions of the KdV equation with varying dispersion, nonlinearity, and gain. Finally, we compare these solutions with the nonautonomous solitons of the NLSE emphasizing their common features.
Pilot-wave hydrodynamics in a rotating frame: Exotic orbits
Oza, Anand U.
We present the results of a numerical investigation of droplets walking on a rotating vibrating fluid bath. The drop's trajectory is described by an integro-differential equation, which is simulated numerically in various ...
Pilot-wave hydrodynamics in a rotating frame: Exotic orbits
Oza, Anand U.; Harris, Daniel M.; Rosales, Rodolfo R.; Bush, John W. M.; Wind-Willassen, Øistein
2014-08-15
We present the results of a numerical investigation of droplets walking on a rotating vibrating fluid bath. The drop's trajectory is described by an integro-differential equation, which is simulated numerically in various parameter regimes. As the forcing acceleration is progressively increased, stable circular orbits give way to wobbling orbits, which are succeeded in turn by instabilities of the orbital center characterized by steady drifting then discrete leaping. In the limit of large vibrational forcing, the walker's trajectory becomes chaotic, but its statistical behavior reflects the influence of the unstable orbital solutions. The study results in a complete regime diagram that summarizes the dependence of the walker's behavior on the system parameters. Our predictions compare favorably to the experimental observations of Harris and Bush [“Droplets walking in a rotating frame: from quantized orbits to multimodal statistics,” J. Fluid Mech. 739, 444–464 (2014)].
Comparative Hydrodynamics of Bacterial Polymorphism
NASA Astrophysics Data System (ADS)
Spagnolie, Saverio E.; Lauga, Eric
2011-02-01
Most bacteria swim through fluids by rotating helical flagella which can take one of 12 distinct polymorphic shapes, the most common of which is the normal form used during forward swimming runs. To shed light on the prevalence of the normal form in locomotion, we gather all available experimental measurements of the various polymorphic forms and compute their intrinsic hydrodynamic efficiencies. The normal helical form is found to be the most efficient of the 12 polymorphic forms by a significant margin—a conclusion valid for both the peritrichous and polar flagellar families, and robust to a change in the effective flagellum diameter or length. Hence, although energetic costs of locomotion are small for bacteria, fluid mechanical forces may have played a significant role in the evolution of the flagellum.
The hydrodynamic theory of detonation
NASA Technical Reports Server (NTRS)
Langweiler, Heinz
1939-01-01
This report derives equations containing only directly measurable constants for the quantities involved in the hydrodynamic theory of detonation. The stable detonation speed, D, is revealed as having the lowest possible value in the case of positive material velocity, by finding the minimum of the Du curve (u denotes the speed of the gases of combustion). A study of the conditions of energy and impulse in freely suspended detonating systems leads to the disclosure of a rarefaction front traveling at a lower speed behind the detonation front; its velocity is computed. The latent energy of the explosive passes into the steadily growing detonation zone - the region between the detonation front and the rarefaction front. The conclusions lead to a new definition of the concept of shattering power. The calculations are based on the behavior of trinitrotoluene.
An introduction to relativistic hydrodynamics
Eric Gourgoulhon
2006-03-05
This lecture provides some introduction to perfect fluid dynamics within the framework of general relativity. The presentation is based on the Carter-Lichnerowicz approach. It has the advantage over the more traditional approach of leading very straightforwardly to important conservation laws, such as the relativistic generalizations of Bernoulli's theorem or Kelvin's circulation theorem. It also permits to get easily first integrals of motion which are particularly useful for computing equilibrium configurations of relativistic stars in rotation or in binary systems. The presentation is relatively self-contained and does not require any a priori knowledge of general relativity. In particular, the three types of derivatives involved in relativistic hydrodynamics are introduced in detail: this concerns the Lie, exterior and covariant derivatives.
Hydrodynamic model for drying emulsions
NASA Astrophysics Data System (ADS)
Feng, Huanhuan; Sprakel, Joris; van der Gucht, Jasper
2015-08-01
We present a hydrodynamic model for film formation in a dense oil-in-water emulsion under a unidirectional drying stress. Water flow through the plateau borders towards the drying end leads to the buildup of a pressure gradient. When the local pressure exceeds the critical disjoining pressure, the water films between droplets break and the droplets coalesce. We show that, depending on the critical pressure and the evaporation rate, the coalescence can occur in two distinct modes. At low critical pressures and low evaporation rates, coalescence occurs throughout the sample, whereas at high critical pressures and high evaporation rate, coalescence occurs only at the front. In the latter case, an oil layer develops on top of the film, which acts as a diffusive barrier and slows down film formation. Our findings, which are summarized in a state diagram for film formation, are in agreement with recent experimental findings.
Deterministic hydrodynamics: Taking blood apart
Davis, John A.; Inglis, David W.; Morton, Keith J.; Lawrence, David A.; Huang, Lotien R.; Chou, Stephen Y.; Sturm, James C.; Austin, Robert H.
2006-01-01
We show the fractionation of whole blood components and isolation of blood plasma with no dilution by using a continuous-flow deterministic array that separates blood components by their hydrodynamic size, independent of their mass. We use the technology we developed of deterministic arrays which separate white blood cells, red blood cells, and platelets from blood plasma at flow velocities of 1,000 ?m/sec and volume rates up to 1 ?l/min. We verified by flow cytometry that an array using focused injection removed 100% of the lymphocytes and monocytes from the main red blood cell and platelet stream. Using a second design, we demonstrated the separation of blood plasma from the blood cells (white, red, and platelets) with virtually no dilution of the plasma and no cellular contamination of the plasma. PMID:17001005
Hydrodynamic enhanced dielectrophoretic particle trapping
Miles, Robin R.
2003-12-09
Hydrodynamic enhanced dielectrophoretic particle trapping carried out by introducing a side stream into the main stream to squeeze the fluid containing particles close to the electrodes producing the dielelectrophoretic forces. The region of most effective or the strongest forces in the manipulating fields of the electrodes producing the dielectrophoretic forces is close to the electrodes, within 100 .mu.m from the electrodes. The particle trapping arrangement uses a series of electrodes with an AC field placed between pairs of electrodes, which causes trapping of particles along the edges of the electrodes. By forcing an incoming flow stream containing cells and DNA, for example, close to the electrodes using another flow stream improves the efficiency of the DNA trapping.
Radiation hydrodynamics in solar flares
Fisher, G.H.
1985-10-18
Solar flares are rather violent and extremely complicated phenomena, and it should be made clear at the outset that a physically complete picture describing all aspects of flares does not exist. From the wealth of data which is available, it is apparent that many different types of physical processes are involved during flares: energetic particle acceleration, rapid magnetohydrodynamic motion of complex field structures, magnetic reconnection, violent mass motion along magnetic field lines, and the heating of plasma to tens of millions of degrees, to name a few. The goal of this paper is to explore just one aspect of solar flares, namely, the interaction of hydrodynamics and radiation processes in fluid being rapidly heated along closed magnetic field lines. The models discussed are therefore necessarily restrictive, and will address only a few of the observed or observable phenomena. 46 refs., 6 figs.
Anomalous hydrodynamics kicks neutron stars
Matthias Kaminski; Christoph F. Uhlemann; Marcus Bleicher; Jürgen Schaffner-Bielich
2014-10-14
Observations show that, at the beginning of their existence, neutron stars are accelerated briskly to velocities of up to $1000$ km/s. We discuss possible mechanisms contributing to these kicks in a systematic effective-field-theory framework. Anomalies of the underlying microscopic theory result in chiral transport terms in the hydrodynamic description, and we identify these as explanation for the drastic acceleration. In the presence of vorticity or a magnetic field, the chiral transport effects cause neutrino emission along the respective axes. In typical scenarios, the transport effect due to the magnetic field turns out to be strong enough to explain the kicks. Mixed gauge-gravitational anomalies enter in a distinct way, and we also discuss their implications.
The hydrodynamics of dolphin drafting
Weihs, Daniel
2004-01-01
Background Drafting in cetaceans is defined as the transfer of forces between individuals without actual physical contact between them. This behavior has long been surmised to explain how young dolphin calves keep up with their rapidly moving mothers. It has recently been observed that a significant number of calves become permanently separated from their mothers during chases by tuna vessels. A study of the hydrodynamics of drafting, initiated in the hope of understanding the mechanisms causing the separation of mothers and calves during fishing-related activities, is reported here. Results Quantitative results are shown for the forces and moments around a pair of unequally sized dolphin-like slender bodies. These include two major effects. First, the so-called Bernoulli suction, which stems from the fact that the local pressure drops in areas of high speed, results in an attractive force between mother and calf. Second is the displacement effect, in which the motion of the mother causes the water in front to move forwards and radially outwards, and water behind the body to move forwards to replace the animal's mass. Thus, the calf can gain a 'free ride' in the forward-moving areas. Utilizing these effects, the neonate can gain up to 90% of the thrust needed to move alongside the mother at speeds of up to 2.4 m/sec. A comparison with observations of eastern spinner dolphins (Stenella longirostris) is presented, showing savings of up to 60% in the thrust that calves require if they are to keep up with their mothers. Conclusions A theoretical analysis, backed by observations of free-swimming dolphin schools, indicates that hydrodynamic interactions with mothers play an important role in enabling dolphin calves to keep up with rapidly moving adult school members. PMID:15132740
Detonation-wave interactions. [PBX-9404
Mader, C.L.
1981-01-01
The interaction of laterally colliding, diverging, cylindrical detonation waves in PBX-9404 has been studied using the radiographic machine PHERMEX and the two-dimensional, reactive Lagrangian hydrodynamic code 2DL. The experimentally observed flow could be numerically reproduced using the Forest Fire heterogeneous shock initiation burn model which permits realistic numerical simulation of the burning region of regular and diverging detonation waves, and the interacting detonation waves undergoing regular and Mach reflection. The interaction of two, three, and five colliding, diverging spherical detonation waves in PBX-9404 has been numerically modeled using the three-dimensional, reactive Eulerian hydrodynamic code 3DE. The size and magnitude of the high pressure double, triple, quadruple, and quintuple interactions depends significantly upon the number and relative locations of initiators. The initiation of propagating detonation in the insensitive explosive PBX-9502 by triple shock-wave interaction resulting from three initiators has been studied using the 3DE code with Forest Fire kinetics.
Early hydrodynamic evolution of a stellar collision
Kushnir, Doron; Katz, Boaz
2014-04-20
The early phase of the hydrodynamic evolution following the collision of two stars is analyzed. Two strong shocks propagate from the contact surface and move toward the center of each star at a velocity that is a small fraction of the velocity of the approaching stars. The shocked region near the contact surface has a planar symmetry and a uniform pressure. The density vanishes at the (Lagrangian) surface of contact, and the speed of sound diverges there. The temperature, however, reaches a finite value, since as the density vanishes, the finite pressure is radiation dominated. For carbon-oxygen white dwarf (CO WD) collisions, this temperature is too low for any appreciable nuclear burning shortly after the collision, which allows for a significant fraction of the mass to be highly compressed to the density required for efficient {sup 56}Ni production in the detonation wave that follows. This property is crucial for the viability of collisions of typical CO WD as progenitors of type Ia supernovae, since otherwise only massive (>0.9 M {sub ?}) CO WDs would have led to such explosions (as required by all other progenitor models). The divergence of the speed of sound limits numerical studies of stellar collisions, as it makes convergence tests exceedingly expensive unless dedicated schemes are used. We provide a new one-dimensional Lagrangian numerical scheme to achieve this. A self-similar planar solution is derived for zero-impact parameter collisions between two identical stars, under some simplifying assumptions (including a power-law density profile), which is the planar version of previous piston problems that were studied in cylindrical and spherical symmetries.
Conservative, special-relativistic smoothed particle hydrodynamics
Rosswog, Stephan
2010-11-01
We present and test a new, special-relativistic formulation of smoothed particle hydrodynamics (SPH). Our approach benefits from several improvements with respect to earlier relativistic SPH formulations. It is self-consistently derived from the Lagrangian of an ideal fluid and accounts for the terms that stem from non-constant smoothing lengths, usually called 'grad-h terms'. In our approach, we evolve the canonical momentum and the canonical energy per baryon and thus circumvent some of the problems that have plagued earlier formulations of relativistic SPH. We further use a much improved artificial viscosity prescription which uses the extreme local eigenvalues of the Euler equations and triggers selectively on (a) shocks and (b) velocity noise. The shock trigger accurately monitors the relative density slope and uses it to fine-tune the amount of artificial viscosity that is applied. This procedure substantially sharpens shock fronts while still avoiding post-shock noise. If not triggered, the viscosity parameter of each particle decays to zero. None of these viscosity triggers is specific to special relativity, both could also be applied in Newtonian SPH. The performance of the new scheme is explored in a large variety of benchmark tests where it delivers excellent results. Generally, the grad-h terms deliver minor, though worthwhile, improvements. As expected for a Lagrangian method, it performs close to perfect in supersonic advection tests, but also in strong relativistic shocks, usually considered a particular challenge for SPH, the method yields convincing results. For example, due to its perfect conservation properties, it is able to handle Lorentz factors as large as {gamma} = 50,000 in the so-called wall shock test. Moreover, we find convincing results in a rarely shown, but challenging test that involves so-called relativistic simple waves and also in multi-dimensional shock tube tests.
Radiative Hydrodynamic Models of Optical and Ultraviolet Emission from M Dwarf Flares
Allred, J C; Carlsson, M; Hawley, S L; Abbett, William P.; Allred, Joel C.; Carlsson, Mats; Hawley, Suzanne L.
2006-01-01
We report on radiative hydrodynamic simulations of M dwarf stellar flares and compare the model predictions to observations of several flares. The flares were simulated by calculating the hydrodynamic response of a model M dwarf atmosphere to a beam of non-thermal electrons. Radiative backwarming through numerous soft X-ray, extreme ultraviolet, and ultraviolet transitions are also included. The equations of radiative transfer and statistical equilibrium are treated in non-LTE for many transitions of hydrogen, helium and the Ca II ion allowing the calculation of detailed line profiles and continuum radiation. Two simulations were carried out, with electron beam fluxes corresponding to moderate and strong beam heating. In both cases we find the dynamics can be naturally divided into two phases: an initial gentle phase in which hydrogen and helium radiate away much of the beam energy, and an explosive phase characterized by large hydrodynamic waves. During the initial phase, lower chromospheric material is evap...
An overview of seismic-induced hydrodynamic phenomena in LMR reactor tanks
Ma, D.C.; Chang, Y.W.; Seidensticker, R.W.
1991-01-01
Liquid metal reactors (LMTs) usually contain a huge volume of liquid sodium as reactor coolant. Since most reactor components are submerged in the sodium coolant, the seismic-induced hydrodynamic effects are of great importance in the design of LMR reactor components. Because LMRs operate at low pressures, the reactor components are made of thin-walled structures. Of interest in reactor design, in particular, are the hydrodynamic pressures imposed on various components, such as the reactor vessel wall, thermal liner, and components projecting down into the liquid sodium. The sloshing wave height and impact forces on the reactor cover are also important in assessing the safety of the reactor system. This paper presents an overview of the seismic-induced hydrodynamic phenomena in the LMR reactor tanks. 10 refs., 14 figs., 2 tabs.
Study of High Mach Number Laser Driven Blast Waves
Edens, A; Ditmire, T; Hansen, J F; Edwards, M J; Adams, R G; Rambo, P; Ruggles, L; Smith, I C; Porter, J L
2004-02-26
The study of blast waves produced by intense lasers in gases is motivated by the desire to explore astrophysically relevant hydrodynamic phenomena in the laboratory. We have performed a systematic scan of laser produced blast waves and have examined the blast wave structure over a wide range of drive laser energy. Lasers with energies ranging from 10J-1000J illuminated a pin target in either xenon or nitrogen gas, creating a spherical blast wave. We observe a strongly radiating blast wave in xenon gas while blast waves in nitrogen more closely approximate a pure Taylor-Sedov wave. We also find that at all laser energies, blast waves traveling through xenon gas had their hydrodynamic evolution significantly affected by the passage of the illumination laser.
A hybrid level set/volume-of-fluid approach for simulation of nearshore hydrodynamics
NASA Astrophysics Data System (ADS)
Bakhtyar, R.; Kees, C. E.; Miller, C. T.; Farthing, M. W.
2013-12-01
Wave breaking can play an important role in hydrodynamics near the coast and subsequently can be a factor in beach morphodynamics. However, an accurate understanding of the wave breaking and mixing of water and air at the free surface has yet to be achieved. Numerical models, based on single phase flow, have been used to study the nearshore hydrodynamics, but air-water two-phase flow is not well understood, and so there is a need for additional investigation into the details of this type of flow. The main objective of this study was to de¬velop further understanding of surf-swash zone hydrodynamics under a variety of wave forcing conditions. The main tool used was a com-prehensive two-phase numerical model - combining two-dimensional wave solver with the state-of-the-art 'Eulerian' technique for free surface modeling- of nearshore hydrodynamics. Surf-swash zone hydrodynamics were modeled using the Navier-Stokes equations, combined with turbulence closure model and a hybrid level set/volume-of-fluid approach. The hybrid level set/volume-of-fluid approach combines the accuracy and conceptual simplicity of front-tracking using level set methods with the conservation properties of volume-of fluid methods. The solver was discretized using a finite element method. The model's grid convergence and refinement were investigated in order to obtain high accuracy at an acceptable computational cost while retain robustness. The numerical set-up was tested against the well-known experimental data, with good agreement found. The numerical results showed that the maximum turbulent kinetic energy, turbulence dissipation rate, and velocity components are located near the free surface in the wave breaking area. The model is appropriate for the simulation of air-water mixing flow, undertow distribution, and turbulence characteristics in the nearshore zone. Generally, the analysis shows that, with reasonable hypotheses, it is possible to simulate the surf-swash zone hydrodynamics under wave breaking, consistent with existing understanding of this area.
Low Mach number fluctuating hydrodynamics of multispecies liquid mixtures
NASA Astrophysics Data System (ADS)
Donev, Aleksandar; Nonaka, Andy; Bhattacharjee, Amit Kumar; Garcia, Alejandro L.; Bell, John B.
2015-03-01
We develop a low Mach number formulation of the hydrodynamic equations describing transport of mass and momentum in a multispecies mixture of incompressible miscible liquids at specified temperature and pressure, which generalizes our prior work on ideal mixtures of ideal gases [Balakrishnan et al., "Fluctuating hydrodynamics of multispecies nonreactive mixtures," Phys. Rev. E 89 013017 (2014)] and binary liquid mixtures [Donev et al., "Low mach number fluctuating hydrodynamics of diffusively mixing fluids," Commun. Appl. Math. Comput. Sci. 9(1), 47-105 (2014)]. In this formulation, we combine and extend a number of existing descriptions of multispecies transport available in the literature. The formulation applies to non-ideal mixtures of arbitrary number of species, without the need to single out a "solvent" species, and includes contributions to the diffusive mass flux due to gradients of composition, temperature, and pressure. Momentum transport and advective mass transport are handled using a low Mach number approach that eliminates fast sound waves (pressure fluctuations) from the full compressible system of equations and leads to a quasi-incompressible formulation. Thermal fluctuations are included in our fluctuating hydrodynamics description following the principles of nonequilibrium thermodynamics. We extend the semi-implicit staggered-grid finite-volume numerical method developed in our prior work on binary liquid mixtures [Nonaka et al., "Low mach number fluctuating hydrodynamics of binary liquid mixtures," arXiv:1410.2300 (2015)] and use it to study the development of giant nonequilibrium concentration fluctuations in a ternary mixture subjected to a steady concentration gradient. We also numerically study the development of diffusion-driven gravitational instabilities in a ternary mixture and compare our numerical results to recent experimental measurements [Carballido-Landeira et al., "Mixed-mode instability of a miscible interface due to coupling between Rayleigh-Taylor and double-diffusive convective modes," Phys. Fluids 25, 024107 (2013)] in a Hele-Shaw cell. We find that giant nonequilibrium fluctuations can trigger the instability but are eventually dominated by the deterministic growth of the unstable mode, in both quasi-two-dimensional (Hele-Shaw) and fully three-dimensional geometries used in typical shadowgraph experiments.
"Oenodynamic": Hydrodynamic of wine swirling
Reclari, Martino; Tissot, Stephanie; Obreschkow, Danail; Wurm, Florian; Farhat, Mohamed
2011-01-01
A crucial step in wine tasting is the so called swirling, necessary to release the bouquet of the wine: a gentle circular movement of the glass generates a wave propagating along the glass walls, enhancing oxygenation and mixing. Although being used in a large variety of other applications (e.g. cells cultures in orbital shaken bioreactors) this motion is not yet well understood. In this fluid dynamics video we show the large variety of waves shapes generated by this simple movement, and we identify a group of dimensionless parameters governing the flow.
Typical geometry of rogue waves
NASA Astrophysics Data System (ADS)
Yudin, Alexander; Shamin, Roman
2015-04-01
Our talk presents geometry results of numerical modeling of rogue waves based on the full nonlinear equations of hydrodynamics. We describe the widespread types of rogue waves in computational experiments. We received a lot of rogue waves in our computing experiments. About 95% of these waves have the typical form of steep ridge ("wall of water"). Other rogue waves have the form of deepest depression ("hole in the sea") or represent several waves of very big height ("three sisters"). Rogue waves from our experiments are one of such individual waves. The most widespread rogue waves have the form of wall of water. Both parts of this wave from the left minimum to the maximum and from the maximum to the right minimum are well-approximated by three-degree polynomials. It gets the follow type after linear transformation when the ordinate of maximum point is transferred to the point with coordinates. References Zakharov V.E., Shamin R.V and Yudin A.V.: Energy Portrait of Rogue Waves, JETP Letters, 2014, Vol. 99, No. 9, pp. 514-517, DOI: 10.1134/S0021364014090136
Hydrodynamic constraints to the seaward development of Posidonia oceanica meadows
NASA Astrophysics Data System (ADS)
Vacchi, Matteo; Montefalcone, Monica; Bianchi, Carlo N.; Morri, Carla; Ferrari, Marco
2012-01-01
Posidonia oceanica, the most important and abundant seagrass in the Mediterranean Sea, forms large meadows from the sea surface down to 40 m. The depth of the lower limit of the meadows marks the boundary between the infralittoral and the circalittoral zone, and is said to be normally set by light attenuation underwater, while the role of water movement has been little explored. In this paper, the position (i.e. distance from the shoreline and depth) of P. oceanica meadow lower limits along the whole Ligurian coastline (about 350 km) was related to the annual storm wave base. This depth represents the limit of interaction between waves and seafloor and corresponds to L0/2, where L0 is the annual offshore wave length. In all meadows, the lower limit has never been found deeper than the annual storm wave base, and its depth ( Z c) showed related to L 0 according to the equation Z c = 0.32• L0 + 5.62. In the coastal tracts affected by the least intense waves, the reduction of water movement with depth represents the most important constraint to the seaward development of the meadow, whereas light availability plays a major role in meadows affected by the most intense waves. The present study represents the first attempt at understanding the role of hydrodynamic factors in setting the depth limit of seagrass meadows. If corroborated by future research at other sites, this will have important implications for both basic and applied science, as it would imply rethinking about the relative importance of water movement and light in seagrass depth distribution, and could allow for a better estimate of the extent of meadow regression in anthropized areas.