Strong nonlinear oscillators analytical solutions
Cveticanin, Livija
2017-01-01
This book outlines an analytical solution procedure of the pure nonlinear oscillator system, offering a solution for free and forced vibrations of the one-degree-of-freedom strong nonlinear system with constant and time variable parameter. Includes exercises.
Strongly nonlinear oscillators analytical solutions
Cveticanin, Livija
2014-01-01
This book provides the presentation of the motion of pure nonlinear oscillatory systems and various solution procedures which give the approximate solutions of the strong nonlinear oscillator equations. The book presents the original author’s method for the analytical solution procedure of the pure nonlinear oscillator system. After an introduction, the physical explanation of the pure nonlinearity and of the pure nonlinear oscillator is given. The analytical solution for free and forced vibrations of the one-degree-of-freedom strong nonlinear system with constant and time variable parameter is considered. Special attention is given to the one and two mass oscillatory systems with two-degrees-of-freedom. The criteria for the deterministic chaos in ideal and non-ideal pure nonlinear oscillators are derived analytically. The method for suppressing chaos is developed. Important problems are discussed in didactic exercises. The book is self-consistent and suitable as a textbook for students and also for profess...
Canonical Transform Method for Treating Strongly Anisotropy Magnets
DEFF Research Database (Denmark)
Cooke, J. F.; Lindgård, Per-Anker
1977-01-01
An infinite-order perturbation approach to the theory of magnetism in magnets with strong single-ion anisotropy is given. This approach is based on a canonical transformation of the system into one with a diagonal crystal field, an effective two-ion anisotropy, and reduced ground-state corrections....... A matrix-element matching procedure is used to obtain an explicit expression for the spin-wave energy to second order. The consequences of this theory are illustrated by an application to a simple example with planar anisotropy and an external magnetic field. A detailed comparison between the results...
High nonlinear optical anisotropy of urea nanofibers
Isakov, D.; de Matos Gomes, E.; Belsley, M.; Almeida, B.; Martins, A.; Neves, N.; Reis, R.
2010-07-01
Nanofibers consisting of the optically nonlinear organic molecule urea embedded in both poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA) polymers were produced by the electrospinning technique. The second-harmonic generation produced by aligned fiber mats of these materials displays a strong dependence on the polarization of the incident light. In PVA-urea nanofibers the effectiveness in generating of the second-harmonic light is as high as that of a pure urea powder with an average grain size of 110 μm. The results suggest that single crystalline urea nanofibers were achieved with a long-range crystalline order extending into the range of 2-4 μm with PVA as the host polymer.
Nonlinear Electron Waves in Strongly Magnetized Plasmas
DEFF Research Database (Denmark)
Pécseli, Hans; Juul Rasmussen, Jens
1980-01-01
dynamics in the analysis is also demonstrated. As a particular case the authors investigate nonlinear waves in a strongly magnetized plasma filled wave-guide, where the effects of finite geometry are important. The relevance of this problem to laboratory experiments is discussed.......Weakly nonlinear dispersive electron waves in strongly magnetized plasma are considered. A modified nonlinear Schrodinger equation is derived taking into account the effect of particles resonating with the group velocity of the waves (nonlinear Landau damping). The possibility of including the ion...
LDA+DMFT Approach to Magnetocrystalline Anisotropy of Strong Magnets
Directory of Open Access Journals (Sweden)
Jian-Xin Zhu
2014-05-01
Full Text Available The new challenges posed by the need of finding strong rare-earth-free magnets demand methods that can predict magnetization and magnetocrystalline anisotropy energy (MAE. We argue that correlated electron effects, which are normally underestimated in band-structure calculations, play a crucial role in the development of the orbital component of the magnetic moments. Because magnetic anisotropy arises from this orbital component, the ability to include correlation effects has profound consequences on our predictive power of the MAE of strong magnets. Here, we show that incorporating the local effects of electronic correlations with dynamical mean-field theory provides reliable estimates of the orbital moment, the mass enhancement, and the MAE of YCo_{5}.
Generalized Strongly Nonlinear Implicit Quasivariational Inequalities
Directory of Open Access Journals (Sweden)
Salahuddin
2009-01-01
Full Text Available We prove an existence theorem for solution of generalized strongly nonlinear implicit quasivariational inequality problems and convergence of iterative sequences with errors, involving Lipschitz continuous, generalized pseudocontractive and generalized -pseudocontractive mappings in Hilbert spaces.
Campanella, H; Jaafar, M; Llobet, J; Esteve, J; Vázquez, M; Asenjo, A; del Real, R P; Plaza, J A
2011-12-16
We report on a new approach for magnetic imaging, highly sensitive even in the presence of external, strong magnetic fields. Based on FIB-assisted fabricated high-aspect-ratio rare-earth nanomagnets, we produce groundbreaking magnetic force tips with hard magnetic character where we combine a high aspect ratio (shape anisotropy) together with strong crystalline anisotropy (rare-earth-based alloys). Rare-earth hard nanomagnets are then FIB-integrated to silicon microcantilevers as highly sharpened tips for high-field magnetic imaging applications. Force resolution and domain reversing and recovery capabilities are at least one order of magnitude better than for conventional magnetic tips. This work opens new, pioneering research fields on the surface magnetization process of nanostructures based either on relatively hard magnetic materials-used in magnetic storage media-or on materials like superparamagnetic particles, ferro/antiferromagnetic structures or paramagnetic materials.
Nonlinear parallel momentum transport in strong turbulence
Wang, Lu; Diamond, P H
2015-01-01
Most existing theoretical studies of momentum transport focus on calculating the Reynolds stress based on quasilinear theory, without considering the \\emph{nonlinear} momentum flux-$$. However, a recent experiment on TORPEX found that the nonlinear toroidal momentum flux induced by blobs makes a significant contribution as compared to the Reynolds stress [Labit et al., Phys. Plasmas {\\bf 18}, 032308 (2011)]. In this work, the nonlinear parallel momentum flux in strong turbulence is calculated by using three dimensional Hasegawa-Mima equation. It is shown that nonlinear diffusivity is smaller than quasilinear diffusivity from Reynolds stress. However, the leading order nonlinear residual stress can be comparable to the quasilinear residual stress, and so could be important to intrinsic rotation in tokamak edge plasmas. A key difference from the quasilinear residual stress is that parallel fluctuation spectrum asymmetry is not required for nonlinear residual stress.
Nonlinear spin control by terahertz-driven anisotropy fields
Baierl, S.; Hohenleutner, M.; Kampfrath, T.; Zvezdin, A. K.; Kimel, A. V.; Huber, R.; Mikhaylovskiy, R. V.
2016-11-01
Future information technologies, such as ultrafast data recording, quantum computation or spintronics, call for ever faster spin control by light. Intense terahertz pulses can couple to spins on the intrinsic energy scale of magnetic excitations. Here, we explore a novel electric dipole-mediated mechanism of nonlinear terahertz-spin coupling that is much stronger than linear Zeeman coupling to the terahertz magnetic field. Using the prototypical antiferromagnet thulium orthoferrite (TmFeO3), we demonstrate that resonant terahertz pumping of electronic orbital transitions modifies the magnetic anisotropy for ordered Fe3+ spins and triggers large-amplitude coherent spin oscillations. This mechanism is inherently nonlinear, it can be tailored by spectral shaping of the terahertz waveforms and its efficiency outperforms the Zeeman torque by an order of magnitude. Because orbital states govern the magnetic anisotropy in all transition-metal oxides, the demonstrated control scheme is expected to be applicable to many magnetic materials.
Nonlinear waves in strongly interacting relativistic fluids
Fogaça, D A; Filho, L G Ferreira
2013-01-01
During the past decades the study of strongly interacting fluids experienced a tremendous progress. In the relativistic heavy ion accelerators, specially the RHIC and LHC colliders, it became possible to study not only fluids made of hadronic matter but also fluids of quarks and gluons. Part of the physics program of these machines is the observation of waves in this strongly interacting medium. From the theoretical point of view, these waves are often treated with li-nearized hydrodynamics. In this text we review the attempts to go beyond linearization. We show how to use the Reductive Perturbation Method to expand the equations of (ideal and viscous) relativistic hydrodynamics to obtain nonlinear wave equations. These nonlinear wave equations govern the evolution of energy density perturbations (in hot quark gluon plasma) or baryon density perturbations (in cold quark gluon plasma and nuclear matter). Different nonlinear wave equations, such as the breaking wave, Korteweg-de Vries and Burgers equations, are...
Strong enhancement of magnetic anisotropy energy in alloyed nanowires
Energy Technology Data Exchange (ETDEWEB)
Negulyaev, Nikolay; Niebergall, Larissa; Stepanyuk, Valeri [Max-Planck-Institut fuer Mikrostrukturphysik, D-06120 Halle (Germany); Juarez Reyes, Lucila; Pastor, Gustavo [Institut fuer Theoretische Physik, Universitaet Kassel, D-34132 Kassel (Germany); Dorantes-Davila, Jesus [Instituto de Fisica, Universidad Autonoma de San Luis Potosi, 78000 San Luis Potosi (Mexico)
2011-07-01
One-dimensional atomic structures (monatomic wires and chains) are believed to be likely candidates for creation of nanostructures with large atomic orbital moments and hence with giant magnetic anisotropy energy (MAE) per atom. We investigate the possibility of tuning the MAE of 3d transition metal monowires alloyed with 5d elements (Ir, Pt). Our ab initio studies give clear evidence that in mixed 3d-5d atomic wires MAE is one and even two orders of magnitude more than in pure wires constructed of the corresponding 5d and 3d elements, respectively. Mechanisms responsible for the formation of such a strong MAE are revealed. The interplay between the structure of a monowire and its MAE is demonstrated. The contribution of both types of species (3d and 5d) into the MAE is discussed.
Heteroclinic Bifurcation of Strongly Nonlinear Oscillator
Institute of Scientific and Technical Information of China (English)
ZHANG Qi-Chang; WANG Wei; LI Wei-Yi
2008-01-01
Analytical prediction of heteroclinic bifurcation of the strongly nonlinear oscillator is presented by using the extended normal form method.We consider the approximate periodic solution of the system subject to the quintic nonlinearity by introducing the undetermined fundamental frequency.For the occurrence of heteroclinicity,the bifurcation criterion is accomplished.It depends on the contact of the limit cycle with the saddle equilibrium.As is illustrated,the explicit application shows that the new results coincide very well with the results of numerical simulation when disturbing parameter is of arbitrary magnitude.PACS: 82.40.Bj,47.20.Ky,02.30.Hq
Strongly nonlinear steepening of long interfacial waves
Directory of Open Access Journals (Sweden)
N. Zahibo
2007-06-01
Full Text Available The transformation of nonlinear long internal waves in a two-layer fluid is studied in the Boussinesq and rigid-lid approximation. Explicit analytic formulation of the evolution equation in terms of the Riemann invariants allows us to obtain analytical results characterizing strongly nonlinear wave steepening, including the spectral evolution. Effects manifesting the action of high nonlinear corrections of the model are highlighted. It is shown, in particular, that the breaking points on the wave profile may shift from the zero-crossing level. The wave steepening happens in a different way if the density jump is placed near the middle of the water bulk: then the wave deformation is almost symmetrical and two phases appear where the wave breaks.
Analytical solution of strongly nonlinear Duffing oscillators
Directory of Open Access Journals (Sweden)
A.M. El-Naggar
2016-06-01
Full Text Available In this paper, a new perturbation technique is employed to solve strongly nonlinear Duffing oscillators, in which a new parameter α=α(ε is defined such that the value of α is always small regardless of the magnitude of the original parameter ε. Therefore, the strongly nonlinear Duffing oscillators with large parameter ε are transformed into a small parameter system with respect to α. Approximate solution obtained by the present method is compared with the solution of energy balance method, homotopy perturbation method, global error minimization method and lastly numerical solution. We observe from the results that this method is very simple, easy to apply, and gives a very good accuracy not only for small parameter εbut also for large values of ε.
β - Ag2Te: A topological insulator with strong anisotropy
Wang, Lan; Sulaev, Azat; Ren, Peng; Xia, Bin; Lin, Qinghua; Yu, Ting; Qiu, Caiyu; Zhang, Shuang-Yuan; Han, Ming-Yong; Li, Zhipeng; Zhu, Wei Guang; Wu, Qingyu; Feng, Yuan Ping; Shen, Lei; Shen, Shun-Qing
2013-03-01
We present evidence of topological surface states in β-Ag2Te through first-principles calculations, periodic quantum interference effect and ambipolar electric field effect in single crystalline nanoribbon. Our first-principles calculations show that β-Ag2Te is a topological insulator with a gapless Dirac cone with strong anisotropy. To experimentally probe the topological surface state, we synthesized high quality β-Ag2Te nanoribbons and performed electron transport measurements. The coexistence of pronounced Aharonov-Bohm oscillations and weak Altshuler-Aronov-Spivak oscillations clearly demonstrates coherent electron transport around the perimeter of β-Ag2Te nanoribbon and therefore the existence of topological surface states, which is further supported by the ambipolar electric field effect for devices fabricated by β-Ag2Te nanoribbons. The experimentally confirmed topological surface states and the theoretically predicted isotropic Dirac cone of β-Ag2Te suggest that the material may be a promising material for fundamental study and future spintronic devices. RCA-08/018 (Singapore), MOE2010-T2-2-059 (Singapore), HKU705150P (Hong Kong), NTU-SUG M4080513
Anisotropies in the microwave sky due to nonlinear structures
Energy Technology Data Exchange (ETDEWEB)
Martinez-Gonzalez, E.; Sanz, J.L.; Silk, J. (California Univ., Berkeley (USA))
1990-05-01
The propagation of light in a nonstatic linear gravitational potential associated with nonlinear density fluctuations is studied. A potential approximation to Einstein's field equations makes it possible to derive simple expressions for the anisotropies induced in the temperature of the microwave background radiation, associated in particular with angular distortions induced by the time-varying gravitational potential along the line of sight to the surface of last scattering. These results are applied to two examples of interest: a compensated void in the thin-shell approximation and a compensated lump in the Swiss cheese approach, obtaining the same results, with regard to temperature profiles, as those obtained using a general-relativistic treatment. 20 refs.
Su, Wei-Jou
This thesis consists of two parts. Part one is concerned with the effect of fault zone heterogeneity on the strong ground motion of the Loma Preita earthquake. Part two is concerned with the effect of the effective hexagonal anisotropy of a fault zone on strong ground motion. A superposition of Gaussian beams is used to analyze these problems because it can account for both the rupture history of the fault plane and the fault zone heterogeneity. We also extend this method to investigate the combined effects of the rupture process on a fault plane and medium anisotropy on the synthetic seismograms. The strong ground motion of the Loma Prieta Earthquake is synthesized using a known three-dimensional crustal model of the region, a rupture model determined under the assumption of laterally homogeneous structure, and Green's functions computed by superposition of Gaussian beams. Compared to results obtained assuming a laterally homogeneous crust, stations lying to the northeast of the rupture zone are predicted to be defocused, while stations lying to the west of the fault trace are predicted to be focused. The defocusing is caused by a zone of high velocity material between the San Andreas and Sargent faults, and the focusing is caused by a region of low velocity lying between the Zayantes and San Andreas faults. If lateral homogeneity is assumed, the net effect of the predicted focusing and defocusing is to bias estimates of the relative slip of two high slip regions found in inversions of local and teleseismic body waves. These biases are similar in magnitude to those estimated for waveform inversions from the effects of using different subsets of data and/or different misfit functions and are similar in magnitude to the effects predicted for non-linear site responses.
Nonlinear Response of Strong Nonlinear System Arisen in Polymer Cushion
Directory of Open Access Journals (Sweden)
Jun Wang
2013-01-01
Full Text Available A dynamic model is proposed for a polymer foam-based nonlinear cushioning system. An accurate analytical solution for the nonlinear free vibration of the system is derived by applying He's variational iteration method, and conditions for resonance are obtained, which should be avoided in the cushioning design.
Energy Method to Obtain Approximate Solutions of Strongly Nonlinear Oscillators
Directory of Open Access Journals (Sweden)
Alex Elías-Zúñiga
2013-01-01
Full Text Available We introduce a nonlinearization procedure that replaces the system potential energy by an equivalent representation form that is used to derive analytical solutions of strongly nonlinear conservative oscillators. We illustrate the applicability of this method by finding the approximate solutions of two strongly nonlinear oscillators and show that this procedure provides solutions that follow well the numerical integration solutions of the corresponding equations of motion.
Strongly Nonlinear Transverse Perturbations in Phononic Crystals
Directory of Open Access Journals (Sweden)
S. Nikitenkova
2014-01-01
Full Text Available The dynamics of the surface heterogeneities formation in low-dimensional phononic crystals is studied. It is shown that phononic transverse perturbations in this medium are highly nonlinear. They can be described with the help of the Riemann wave and may form stable wave structures of the finite amplitude. The Riemann wave deformation is described analytically. The Riemann wave time existence up to the beginning of the gradient catastrophe is calculated.
Nonlinear magnetoplasmons in strongly coupled Yukawa plasmas
Bonitz, M; Ott, T; Kaehlert, H; Hartmann, P
2010-01-01
The existence of plasma oscillations at multiples of the magnetoplasmon frequency in a strongly coupled two-dimensional magnetized Yukawa plasma is reported, based on extensive molecular dynamics simulations. These modes are the analogues of Bernstein modes which are renormalized by strong interparticle correlations. Their properties are theoretically explained by a dielectric function incorporating the combined effect of a magnetic field, strong correlations and finite temperature.
Strong crustal seismic anisotropy in the Kalahari Craton based on Receiver Functions
DEFF Research Database (Denmark)
Thybo, Hans; Soliman, Mohammad Youssof Ahmad; Artemieva, Irina
2015-01-01
Earlier seismic studies of the Kalahari Craton in southern Africa infer deformation of upper mantle by flow with fast direction of seismic anisotropy being parallel to present plate motion, and/or report anisotropy frozen into the lithospheric mantle. We present evidence for very strong seismic...... is uniform within tectonic units and parallel to orogenic strike in the Limpopo and Cape fold belts. It is further parallel to the strike of major dyke swarms which indicates that a large part of the observed anisotropy is controlled by lithosphere fabrics and macroscopic effects. The directions of the fast...... that the crust and lithospheric mantle may have been coupled since cratonisation. If so, the apparent match between mantle anisotropy and the present plate motion is coincidental....
Strong crustal seismic anisotropy in the Kalahari Craton based on Receiver Functions
DEFF Research Database (Denmark)
Thybo, Hans; Soliman, Mohammad Youssof Ahmad; Artemieva, Irina
2015-01-01
Earlier seismic studies of the Kalahari Craton in southern Africa infer deformation of upper mantle by flow with fast direction of seismic anisotropy being parallel to present plate motion, and/or report anisotropy frozen into the lithospheric mantle. We present evidence for very strong seismic...... is uniform within tectonic units and parallel to orogenic strike in the Limpopo and Cape fold belts. It is further parallel to the strike of major dyke swarms which indicates that a large part of the observed anisotropy is controlled by lithosphere fabrics and macroscopic effects. The directions of the fast...... that the crust and lithospheric mantle may have been coupled since cratonisation. If so, the apparent match between mantle anisotropy and the present plate motion is coincidental....
Wave Propagation In Strongly Nonlinear Two-Mass Chains
Wang, Si Yin; Herbold, Eric B.; Nesterenko, Vitali F.
2010-05-01
We developed experimental set up that allowed the investigation of propagation of oscillating waves generated at the entrance of nonlinear and strongly nonlinear two-mass granular chains composed of steel cylinders and steel spheres. The paper represents the first experimental data related to the propagation of these waves in nonlinear and strongly nonlinear chains. The dynamic compressive forces were detected using gauges imbedded inside particles at depths equal to 4 cells and 8 cells from the entrance gauge detecting the input signal. At these relatively short distances we were able to detect practically perfect transparency at low frequencies and cut off effects at higher frequencies for nonlinear and strongly nonlinear signals. We also observed transformation of oscillatory shocks into monotonous shocks. Numerical calculations of signal transformation by non-dissipative granular chains demonstrated transparency of the system at low frequencies and cut off phenomenon at high frequencies in reasonable agreement with experiments. Systems which are able to transform nonlinear and strongly nonlinear waves at small sizes of the system are important for practical applications such as attenuation of high amplitude pulses.
Phase field model for strong anisotropy of kinetic and highly anisotropic interfacial energy
Institute of Scientific and Technical Information of China (English)
ZHANG Guo-wei; HOU Hua; CHENG Jun
2006-01-01
A phase-field model was established for simulating pure materials, which was calculated effectively and taken into account the strong anisotropy of kinetic and highly anisotropic interfacial energy. The anisotropy (strong kinetic and highly interfacial energy) of various degrees was simulated with numerical calculation. During a variety of interfacial anisotropy coefficient, equilibrium crystal shape varies from smoothness to corner. There has a critical value during the course of the transformation. When the anisotropy coefficenct is lower than the critical value, the growth velocity v increases monotonically with the increase of it. Whereas the anisotropy coefficent is higher than the critical value, the growth velocity decreases with the increases of it. During a variety of degree of supercooling, the growth velocity is under control from thermal diffusion to kinetics. Under the control of thermal diffusion, the growth velocity increases with the increase of degree of supercooling and tip radius R decreases with the increase of temperature. Under the control of kinetics, with the increase of degree of supercooling both V and R, which can not fit the traditional microcosmic theory.
Rapoport, Yu G.; Boardman, A. D.; Grimalsky, V. V.; Ivchenko, V. M.; Kalinich, N.
2014-05-01
The idea of nonlinear ‘transformation optics-inspired’ [1-6] electromagnetic cylindrical field concentrators has been taken up in a preliminary manner in a number of conference reports [7-9]. Such a concentrator includes both external linear region with a dielectric constant increased towards the centre and internal region with nonlinearity characterized by constant coefficients. Then, in the process of farther investigations we realized the following factors considered neither in [7-9] nor in the recent paper [10]: saturation of nonlinearity, nonlinear losses, linear gain, numerical convergence, when nonlinear effect becomes very strong and formation of ‘hotspots’ starts. It is clearly demonstrated here that such a strongly nonlinear process starts when the nonlinear amplitude of any incident beam(s) exceeds some ‘threshold’ value. Moreover, it is shown that the formation of hotspots may start as the result of any of the following processes: an increase of the input amplitude, increasing the linear amplification in the central nonlinear region, decreasing the nonlinear losses, a decrease in the saturation of the nonlinearity. Therefore, a tendency to a formation of ‘hotspots’ is a rather universal feature of the strongly nonlinear behaviour of the ‘nonlinear resonator’ system, while at the same time the system is not sensitive to the ‘prehistory’ of approaching nonlinear threshold intensity (amplitude). The new proposed method includes a full-wave nonlinear solution analysis (in the nonlinear region), a new form of complex geometric optics (in the linear inhomogeneous external cylinder), and new boundary conditions, matching both solutions. The observed nonlinear phenomena will have a positive impact upon socially and environmentally important devices of the future. Although a graded-index concentrator is used here, it is a direct outcome of transformation optics. Numerical evaluations show that for known materials these nonlinear effects
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The apparent resistivity data of 11 stations observed in or near the epicentral regions for 6 strong earthquakes are processed by the normalized monthly rate method. The result show that in the medium-short and short-imminent terms of earthquake preparation the variation rate of apparent resistivity perpendicular (or near perpendicular) to the direction of maximum principal stress is greater than that parallel (or near parallel) to the direction. Such an-isotropic phenomenon is interpreted as follow: the predominant alignment of cracks containing conductive fluid in the maximum principal stress direction caused the anisotropy of the fluid migration during the dilatancy process in the late period of earthquake preparation and resulted in the anisotropy of true resistivity variation rate for rock (or solid) medium which induced the variation rate anisotropy of apparent resistivity on the ground. The study of this paper provides some seismic examples to show the apparent resistivity anisotropy which may be helpful to study the stress status in or near the source zone in the late period of earthquake preparation of strong events.
Short Pulse Dynamics in Strongly Nonlinear Dissipative Granular Chains
Rosas, Alexandre; Romero, Aldo H.; Nesterenko, Vitali F.; Lindenberg, Katja
2008-01-01
We study the energy decay properties of a pulse propagating in a strongly nonlinear granular chain with damping proportional to the relative velocity of the grains. We observe a wave disturbance that at low viscosities consists of two parts exhibiting two entirely different time scales of dissipation. One part is an attenuating solitary wave, is dominated by discreteness and nonlinearity effects as in a dissipationless chain, and has the shorter lifetime. The other is a purely dissipative sho...
Bifurcations of a parametrically excited oscillator with strong nonlinearity
Institute of Scientific and Technical Information of China (English)
唐驾时; 符文彬; 李克安
2002-01-01
A parametrically excited oscillator with strong nonlinearity, including van der Poi and Duffing types, is studied for static bifurcations. The applicable range of the modified Lindstedt-Poincaré method is extended to 1/2 subharmonic resonance systems. The bifurcation equation of a strongly nonlinear oscillator, which is transformed into a small parameter system, is determined by the multiple scales method. On the basis of the singularity theory, the transition set and the bifurcation diagram in various regions of the parameter plane are analysed.
High-codimensional static bifurcations of strongly nonlinear oscillator
Institute of Scientific and Technical Information of China (English)
Zhang Qi-Chang; Wang Wei; Liu Fu-Hao
2008-01-01
The static bifurcation of the parametrically excited strongly nonlinear oscillator is studied.We consider the averaged equations of a system subject to Duffing-van der Pol and quintic strong nonlinearity by introducing the undetermined fundamental frequency into the computation in the complex normal form.To discuss the static bifurcation,the bifurcation problem is described as a 3-codimensional unfolding with Z2 symmetry on the basis of singularity theory.The transition set and bifurcation diagrams for the singularity are presented,while the stability of the zero solution is studied by using the eigenvalues in various parameter regions.
Nonlinear Dynamics and Strong Cavity Cooling of Levitated Nanoparticles
Fonseca, P. Z. G.; Aranas, E. B.; Millen, J.; Monteiro, T. S.; Barker, P. F.
2016-10-01
Optomechanical systems explore and exploit the coupling between light and the mechanical motion of macroscopic matter. A nonlinear coupling offers rich new physics, in both quantum and classical regimes. We investigate a dynamic, as opposed to the usually studied static, nonlinear optomechanical system, comprising a nanosphere levitated in a hybrid electro-optical trap. The cavity offers readout of both linear-in-position and quadratic-in-position (nonlinear) light-matter coupling, while simultaneously cooling the nanosphere, for indefinite periods of time and in high vacuum. We observe the cooling dynamics via both linear and nonlinear coupling. As the background gas pressure was lowered, we observed a greater than 1000-fold reduction in temperature before temperatures fell below readout sensitivity in the present setup. This Letter opens the way to strongly coupled quantum dynamics between a cavity and a nanoparticle largely decoupled from its environment.
Strength of anisotropy in a granular material: Linear versus nonlinear contact model.
La Ragione, Luigi; Gammariello, Marica; Recchia, Giuseppina
2016-12-01
In this paper, we deal with anisotropy in an idealized granular material made of a collection of frictional, elastic, contacting particles. We present a theoretical analysis for an aggregate of particles isotropically compressed and then sheared, in which two possible contacts laws between particles are considered: a linear contact law, where the contact stiffness is constant; and a nonlinear contact law, where the contact stiffness depends on the overlapping between particles. In the former case the anisotropy observed in the aggregate is associated with particle arrangement. In fact, although the aggregate is initially characterized by an isotropic network of contacts, during the loading, an anisotropic texture develops, which is measured by a fabric tensor. With a nonlinear contact law it is possible to develop anisotropy because contacting stiffnesses are different, depending on the orientation of the contact vectors with respect to the axis of the applied deformation. We find that before the peak load is reached, an aggregate made of particles with a linear contact law develops a much smaller anisotropy compared with that of an aggregate with a nonlinear law.
Strength of anisotropy in a granular material: Linear versus nonlinear contact model
La Ragione, Luigi; Gammariello, Marica; Recchia, Giuseppina
2016-12-01
In this paper, we deal with anisotropy in an idealized granular material made of a collection of frictional, elastic, contacting particles. We present a theoretical analysis for an aggregate of particles isotropically compressed and then sheared, in which two possible contacts laws between particles are considered: a linear contact law, where the contact stiffness is constant; and a nonlinear contact law, where the contact stiffness depends on the overlapping between particles. In the former case the anisotropy observed in the aggregate is associated with particle arrangement. In fact, although the aggregate is initially characterized by an isotropic network of contacts, during the loading, an anisotropic texture develops, which is measured by a fabric tensor. With a nonlinear contact law it is possible to develop anisotropy because contacting stiffnesses are different, depending on the orientation of the contact vectors with respect to the axis of the applied deformation. We find that before the peak load is reached, an aggregate made of particles with a linear contact law develops a much smaller anisotropy compared with that of an aggregate with a nonlinear law.
ELECTROSTATIC POTENTIAL OF STRONGLY NONLINEAR COMPOSITES: HOMOTOPY CONTINUATION APPROACH
Institute of Scientific and Technical Information of China (English)
Wei En-bo; Gu Guo-qing
2000-01-01
The homotopy continuation method is used to solve the electrostaticboundary-value problems of strongly nonlinear composite media, whichobey a current-field relation of J= E+ |E|2E. With the modeexpansion, the approximate analytical solutions of electric potential inhost and inclusion regions are obtained by solving a set of nonlinearordinary different equations, which are derived from the originalequations with homotopy method. As an example in dimension two, we applythe method to deal with a nonlinear cylindrical inclusion embedded in ahost. Comparing the approximate analytical solution of the potentialobtained by homotopy method with that of numerical method, we canobverse that the homotopy method is valid for solving boundary-valueproblems of weakly and strongly nonlinear media.
A simple harmonic balance method for solving strongly nonlinear oscillators
Directory of Open Access Journals (Sweden)
Md. Abdur Razzak
2016-10-01
Full Text Available In this paper, a simple harmonic balance method (HBM is proposed to obtain higher-order approximate periodic solutions of strongly nonlinear oscillator systems having a rational and an irrational force. With the proposed procedure, the approximate frequencies and the corresponding periodic solutions can be easily determined. It gives high accuracy for both small and large amplitudes of oscillations and better result than those obtained by other existing results. The main advantage of the present method is that its simplicity and the second-order approximate solutions almost coincide with the corresponding numerical solutions (considered to be exact. The method is illustrated by examples. The present method is very effective and convenient method for solving strongly nonlinear oscillator systems arising in nonlinear science and engineering.
Spontaneous generation of a temperature anisotropy in a strongly coupled magnetized plasma
Ott, T; Hartmann, P; Donkó, Z
2016-01-01
A magnetic field was recently shown to enhance field-parallel heat conduction in a strongly correlated plasma whereas cross-field conduction is reduced. Here we show that in such plasmas, the magnetic field has the additional effect of inhibiting the isotropization process between field-parallel and cross-field temperature components thus leading to the emergence of strong and long-lived temperature anisotropies when the plasma is locally perturbed. An extended heat equation is shown to describe this process accurately.
Strong axial anisotropy of the magnetic penetration length in superconducting UPt{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Yaouanc, A.; Dalmas de Reotier, P.; Huxley, A.; Flouquet, J. [Commissariat a l' Energie Atomique, Departement de Recherche Fondamentale sur la Matiere Condensee, F-38054 Grenoble Cedex 9 (France); Bonville, P. [Commissariat a l' Energie Atomique, Departement de Recherche sur l' Etat Condense, les Atomes et les Molecules, F-91191 Gif-sur-Yvette (France); Gubbens, P.C.M.; Mulders, A.M. [Interfacultair Reactor Instituut, Delft University of Technology, 2629 JB Delft (Netherlands)
1998-11-02
We report muon spin rotation measurements of the temperature dependence and anisotropy of the magnetic field penetration lengths in the heavy fermion superconductor UPt{sub 3}. We observe a strong axial anisotropy. At 0.05 K we obtain for the penetration length parallel and perpendicular to the c axis {lambda}{sub c} = 4260 (150) A and {lambda}{sub a} = 6040 (130) A respectively. {lambda}{sub a}{sup -2}(T) at low temperatures excludes a superconducting order parameter in the B phase with only a line of nodes in the equatorial plane of the Fermi surface. The combined analysis of {lambda}{sub c}{sup -2}(T) and {lambda}{sub a}{sup -2}(T) measured in the B phase favours an hybrid order parameter with point nodes at the poles and a line of nodes at the equatorial plane. The A phase is characterized by a larger density of nodes than the B phase. (author)
Short-pulse dynamics in strongly nonlinear dissipative granular chains.
Rosas, Alexandre; Romero, Aldo H; Nesterenko, Vitali F; Lindenberg, Katja
2008-11-01
We study the energy decay properties of a pulse propagating in a strongly nonlinear granular chain with damping proportional to the relative velocity of the grains. We observe a wave disturbance that at low viscosities consists of two parts exhibiting two entirely different time scales of dissipation. One part is an attenuating solitary wave, dominated by discreteness and nonlinearity effects as in a dissipationless chain, and has the shorter lifetime. The other is a purely dissipative shocklike structure with a much longer lifetime and exists only in the presence of dissipation. The range of viscosities and initial configurations that lead to this complex wave disturbance are explored.
New Evidence for Nonlinearity in Strong Ground Motion
Beroza, G. C.; Schaff, D. P.
2001-12-01
Dynamic strains associated with the strong ground motion of large earthquakes are well within the regime found to show nonlinearity in the laboratory; however, evidence for nonlinearity in recorded seismic waves is often ambiguous and controversial. We present new and independent evidence that nonlinearity in strong ground motion may be widespread. The evidence consists of velocity changes measured by repeating microearthquakes in the aftermath of the 1984 M=6.2 Morgan Hill and 1989 M=6.9 Loma Prieta events. We have identified over 20 sets of repeating earthquakes in the aftershock zones of these mainshocks that contain up to 40 repeats of the same event. Waveform analysis reveals clearly detectable delays of arrivals from events after the Loma Prieta earthquake, compared with events before, of as much as 3.5% in the early S-wave coda. Source array analysis and waveform similarity over a wide range of source-receiver distances both suggest that the early coda is generated by scattering in the shallow crust near the receiver. We find that the magnitude of the velocity change decreases logarithmically in time following the Loma Prieta mainshock. We have not yet recovered repeating earthquake seismograms from before the Morgan Hill earthquake; however, we observe a clear post-seismic increase in velocity, again with a logarithmic time dependence, suggesting that the same effect accompanied both events. Recent experiments indicate that velocity decreases followed by logarithmic recovery in time accompany recoverable nonlinearity in laboratory samples at ambient conditions [Ten Cate et al., 2000]. Thus, we believe that we have detected the lingering effects of nonlinear mainshock strong ground motion in the time-varying wave propagation characteristics of the Earth's crust. The changes are strongly concentrated near the rupture zones of the two mainshocks; however, the effect is also observed at more distant stations. We use our observations to illuminate the possible
Cyclotron maser emission from power-law electrons with strong pitch-angle anisotropy
Zhao, G Q; Wu, D J; Chen, L; Tang, J F; Liu, Q
2016-01-01
Energetic electrons with power-law spectrum are most commonly observed in astrophysics. This paper investigates electron cyclotron maser emission (ECME) from the power-law electrons, in which strong pitch-angle anisotropy is emphasized. The electron distribution function proposed in this paper can describe various types of pitch-angle anisotropy. Results show that the emission properties of ECME, including radiation growth, propagation, and frequency properties, depend considerably on the types of electron pitch-angle anisotropy, and different wave modes show different dependences on the pitch angle of electrons. In particular, the maximum growth rate of X2 mode rapidly decreases with respect to the electron pitch-angle cosine $\\mu_0$ at which the electron distribution peaks, while the growth rates for other modes (X1, O1, O2) initially increase before decreasing as $\\mu_0$ increases. Moreover, the O mode as well as the X mode can be the fastest growth mode, in terms of not only the plasma parameter but also ...
Off-specular polarized neutron reflectometry study of magnetic dots with a strong shape anisotropy
Temst, K; Moshchalkov, V V; Bruynseraede, Y; Fritzsche, H; Jonckheere, R
2002-01-01
We have measured the off-specular polarized neutron reflectivity of a regular array of rectangular magnetic polycrystalline Co dots, which were prepared by a combination of electron-beam lithography, molecular beam deposition, and lift-off processes. The dots have a length-to-width ratio of 4:1 imposing a strong shape anisotropy. The intensity of the off-specular satellite reflection was monitored as a function of the magnetic field applied parallel to the rows of dots and in the plane of the sample, allowing us to analyze the magnetization-reversal process using the four spin-polarized cross sections. (orig.)
Paradoxical stabilization of forced oscillations by strong nonlinear friction
Esirkepov, Timur Zh.; Bulanov, Sergei V.
2017-08-01
In a dissipative dynamic system driven by an oscillating force, a strong nonlinear highly oscillatory friction force can create a quasi-steady tug, which is always directed opposite to the ponderomotive force induced due to a spatial inhomogeneity of oscillations. When the friction-induced tug exceeds the ponderomotive force, the friction stabilizes the system oscillations near the maxima of the oscillation spatial amplitude of the driving force.
Avetissian, Hamlet
2006-01-01
This book covers a large class of fundamental investigations into Relativistic Nonlinear Electrodynamics. It explores the interaction between charged particles and strong laser fields, mainly concentrating on contemporary problems of x-ray lasers, new type small set-up high-energy accelerators of charged particles, as well as electron-positron pair production from super powerful laser fields of relativistic intensities. It will also discuss nonlinear phenomena of threshold nature that eliminate the concurrent inverse processes in the problems of Laser Accelerator and Free Electron Laser, thus creating new opportunities for solving these problems.
Strong electronic correlation effects in coherent multidimensional nonlinear optical spectroscopy.
Karadimitriou, M E; Kavousanaki, E G; Dani, K M; Fromer, N A; Perakis, I E
2011-05-12
We discuss a many-body theory of the coherent ultrafast nonlinear optical response of systems with a strongly correlated electronic ground state that responds unadiabatically to photoexcitation. We introduce a truncation of quantum kinetic density matrix equations of motion that does not rely on an expansion in terms of the interactions and thus applies to strongly correlated systems. For this we expand in terms of the optical field, separate out contributions to the time-evolved many-body state due to correlated and uncorrelated multiple optical transitions, and use "Hubbard operator" density matrices to describe the exact dynamics of the individual contributions within a subspace of strongly coupled states, including "pure dephasing". Our purpose is to develop a quantum mechanical tool capable of exploring how, by coherently photoexciting selected modes, one can trigger nonlinear dynamics of strongly coupled degrees of freedom. Such dynamics could lead to photoinduced phase transitions. We apply our theory to the nonlinear response of a two-dimensional electron gas (2DEG) in a magnetic field. We coherently photoexcite the two lowest Landau level (LL) excitations using three time-delayed optical pulses. We identify some striking temporal and spectral features due to dynamical coupling of the two LLs facilitated by inter-Landau-level magnetoplasmon and magnetoroton excitations and compare to three-pulse four-wave-mixing (FWM) experiments. We show that these features depend sensitively on the dynamics of four-particle correlations between an electron-hole pair and a magnetoplasmon/magnetoroton, reminiscent of exciton-exciton correlations in undoped semiconductors. Our results shed light into unexplored coherent dynamics and relaxation of the quantum Hall system (QHS) and can provide new insight into non-equilibrium co-operative phenomena in strongly correlated systems.
Methodology for nonlinear quantification of a flexible beam with a local, strong nonlinearity
Herrera, Christopher A.; McFarland, D. Michael; Bergman, Lawrence A.; Vakakis, Alexander F.
2017-02-01
This study presents a methodology for nonlinear quantification, i.e., the identification of the linear and nonlinear regimes and estimation of the degree of nonlinearity, for a cantilever beam with a local, strongly nonlinear stiffness element. The interesting feature of this system is that it behaves linearly in the limits of extreme values of the nonlinear stiffness. An Euler-Bernoulli cantilever beam with two nonlinear configurations is used to develop and demonstrate the methodology. One configuration considers a cubic spring attached at a distance from the beam root to achieve a smooth nonlinear effect. The other configuration considers a vibro-impact element that generates non-smooth effects. Both systems have the property that, in the limit of small and large values of a configuration parameter, the system is almost linear and can be modeled as such with negligible error. For the beam with a cubic spring attachment, the forcing amplitude is the varied parameter, while for the vibro-impact beam, this parameter is the clearance between the very stiff stops and the beam at static equilibrium. Proper orthogonal decomposition is employed to obtain an optimal orthogonal basis used to describe the nonlinear system dynamics for varying parameter values. The frequencies of the modes that compose the basis are then estimated using the Rayleigh quotient. The variations of these frequencies are studied to identify parameter values for which the system behaves approximately linearly and those for which the dynamical response is highly nonlinear. Moreover, a criterion based on the Betti-Maxwell reciprocity theorem is used to verify the existence of nonlinear behavior for the set of parameter values suggested by the described methodology. The developed methodology is general and applicable to discrete or continuous systems with smooth or nonsmooth nonlinearities.
Wan, W. M. V.; Lee, H. C.; Hui, P. M.; Yu, K. W.
1996-08-01
The effective response of random media consisting of two different kinds of strongly nonlinear materials with strong power-law nonlinearity is studied. Each component satisfies current density and electric-field relation of the form J=χ\\|E\\|βE. A simple self-consistent mean-field theory, which leads to a simple way in determining the average local electric field in each constituent, is introduced. Each component is assumed to have a conductivity depending on the averaged local electric field. The averaged local electric field is then determined self-consistently. Numerical simulations of the system are carried out on random nonlinear resistor networks. Theoretical results are compared with simulation data, and excellent agreements are found. Results are also compared with the Hashin-Shtrikman lower bound proposed by Ponte Castaneda et al. [Phys. Rev. B 46, 4387 (1992)]. It is found that the present theory, at small contrasts of χ between the two components, gives a result identical to that of Ponte Castaneda et al. up to second order of the contrast. The crossover and scaling behavior of the effective response near the percolation threshold as suggested by the present theory are discussed and demonstrated.
Effect of geometric anisotropy on optical nonlinearity enhancement for periodic composites
Yang, Baifeng; Zhang, Chengxiang; Tian, Decheng
2003-01-01
The effect of geometric anisotropy on the optical nonlinearity enhancement for the composites with metal or semiconductor spheriodal-shaped particles periodically in an insulating host is investigated. The frequency dependences of effective nonlinear susceptibility are calculated with the Stroud-Hui relation and a series expression of space-dependent electric field in periodic composites. The results show that for both metal-insulator (MI) and semiconductor-insulator (SI) composites, nonlinearity enhancement increases almost to its maximum when the percolation networks of the inclusion phase form. The nonlinearity enhancement increases to its maximum when the composites are transformed into the Boyd-Sipe layered composites. The behavior of the nonlinearity enhancement near the percolation threshold is also investigated. A local minimum appears in the nonlinear optical responses at the percolation threshold for the MI composites. For the SI composites the local minimum appears when the ratio of the bound-electron number density to the effective mass of the electron is large.
Response of MDOF strongly nonlinear systems to fractional Gaussian noises
Deng, Mao-Lin; Zhu, Wei-Qiu
2016-08-01
In the present paper, multi-degree-of-freedom strongly nonlinear systems are modeled as quasi-Hamiltonian systems and the stochastic averaging method for quasi-Hamiltonian systems (including quasi-non-integrable, completely integrable and non-resonant, completely integrable and resonant, partially integrable and non-resonant, and partially integrable and resonant Hamiltonian systems) driven by fractional Gaussian noise is introduced. The averaged fractional stochastic differential equations (SDEs) are derived. The simulation results for some examples show that the averaged SDEs can be used to predict the response of the original systems and the simulation time for the averaged SDEs is less than that for the original systems.
Robust stabilization of uncertain nonholonomic systems with strong nonlinear drifts
Institute of Scientific and Technical Information of China (English)
Yuqiang WU; Xiuyun ZHENG
2008-01-01
This paper investigates the robust stabilization of the nonholonomic control systems with strongly nonlinear uncertainties.In order to make the state scaling effective and to prevent the fiflite time escape phenomenon from happening.the switching control strategy based on the state measurement of the first subsystem is employed to achieve the asymptotic stabilization.The recurslve integrator backstepping technique is applied to the design of the robust controller.The simulation example demonstrates the efficiency and robust features of the proposed method.
Response of MDOF strongly nonlinear systems to fractional Gaussian noises
Energy Technology Data Exchange (ETDEWEB)
Deng, Mao-Lin; Zhu, Wei-Qiu, E-mail: wqzhu@zju.edu.cn [Department of Mechanics, State Key Laboratory of Fluid Power and Mechatronic Systems, Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Zhejiang University, Hangzhou 310027 (China)
2016-08-15
In the present paper, multi-degree-of-freedom strongly nonlinear systems are modeled as quasi-Hamiltonian systems and the stochastic averaging method for quasi-Hamiltonian systems (including quasi-non-integrable, completely integrable and non-resonant, completely integrable and resonant, partially integrable and non-resonant, and partially integrable and resonant Hamiltonian systems) driven by fractional Gaussian noise is introduced. The averaged fractional stochastic differential equations (SDEs) are derived. The simulation results for some examples show that the averaged SDEs can be used to predict the response of the original systems and the simulation time for the averaged SDEs is less than that for the original systems.
Response of MDOF strongly nonlinear systems to fractional Gaussian noises.
Deng, Mao-Lin; Zhu, Wei-Qiu
2016-08-01
In the present paper, multi-degree-of-freedom strongly nonlinear systems are modeled as quasi-Hamiltonian systems and the stochastic averaging method for quasi-Hamiltonian systems (including quasi-non-integrable, completely integrable and non-resonant, completely integrable and resonant, partially integrable and non-resonant, and partially integrable and resonant Hamiltonian systems) driven by fractional Gaussian noise is introduced. The averaged fractional stochastic differential equations (SDEs) are derived. The simulation results for some examples show that the averaged SDEs can be used to predict the response of the original systems and the simulation time for the averaged SDEs is less than that for the original systems.
Nonlinear Principal Component Analysis Using Strong Tracking Filter
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The paper analyzes the problem of blind source separation (BSS) based on the nonlinear principal component analysis (NPCA) criterion. An adaptive strong tracking filter (STF) based algorithm was developed, which is immune to system model mismatches. Simulations demonstrate that the algorithm converges quickly and has satisfactory steady-state accuracy. The Kalman filtering algorithm and the recursive leastsquares type algorithm are shown to be special cases of the STF algorithm. Since the forgetting factor is adaptively updated by adjustment of the Kalman gain, the STF scheme provides more powerful tracking capability than the Kalman filtering algorithm and recursive least-squares algorithm.
Pulsatile instability in rapid directional solidification - Strongly-nonlinear analysis
Merchant, G. J.; Braun, R. J.; Brattkus, K.; Davis, S. H.
1992-01-01
In the rapid directional solidification of a dilute binary alloy, analysis reveals that, in addition to the cellular mode of Mullins and Sekerka (1964), there is an oscillatory instability. For the model analyzed by Merchant and Davis (1990), the preferred wavenumber is zero; the mode is one of pulsation. Two strongly nonlinear analyses are performed that describe this pulsatile mode. In the first case, nonequilibrium effects that alter solute rejection at the interface are taken asymptotically small. A nonlinear oscillator equation governs the position of the solid-liquid interface at leading order, and amplitude and phase evolution equations are derived for the uniformly pulsating interface. The analysis provides a uniform description of both subcritical and supercritical bifurcation and the transition between the two. In the second case, nonequilibrium effects that alter solute rejection are taken asymptotically large, and a different nonlinear oscillator equation governs the location of the interface to leading order. A similar analysis allows for the derivation of an amplitude evolution equation for the uniformly pulsating interface. In this case, the bifurcation is always supercritical. The results are used to make predictions about the characteristics of solute bands that would be frozen into the solid.
Nonlinear phononics and structural control of strongly correlated materials
Energy Technology Data Exchange (ETDEWEB)
Mankowsky, Roman
2016-01-20
Mid-infrared light pulses can be used to resonantly excite infrared-active vibrational modes for the phase control of strongly correlated materials on subpicosecond timescales. As the energy is transferred directly into atomic motions, dissipation into the electronic system is reduced, allowing for the emergence of unusual low energy collective properties. Light-induced superconductivity, insulator-metal transitions and melting of magnetic order demonstrate the potential of this method. An understanding of the mechanism, by which these transitions are driven, is however missing. The aim of this work is to uncover this process by investigating the nonlinear lattice dynamics induced by the excitation and to elucidate their contribution to the modulation of collective properties of strongly correlated materials. The first signature of nonlinear lattice dynamics was reported in the observation of coherent phonon oscillations, resonant with the excitation of an infrared-active phonon mode in a manganite. This nonlinear phononic coupling can be described within a model, which predicts not only oscillatory coherent phonons dynamics but also directional atomic displacements along the coupled modes on average, which could cause the previously observed transitions. We verified this directional response and quantified the anharmonic coupling constant by tracing the atomic motions in a time-resolved hard X-ray diffraction experiment with sub-picometer spatial and femtosecond temporal resolution. In a subsequent study, we investigated the role of nonlinear lattice dynamics in the emergence of superconductivity far above the equilibrium transition temperature, an intriguing effect found to follow lattice excitation of YBa{sub 2}Cu{sub 3}O{sub 6+x}. By combining density functional theory (DFT) calculations of the anharmonic coupling constants with time-resolved X-ray diffraction experiments, we identified a structural rearrangement, which appears and decays with the same temporal
Structural origin for the local strong anisotropy in melt-spun Fe-Ga-Tb: Tetragonal nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Ma, Tianyu, E-mail: maty@zju.edu.cn [State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Key Laboratory of Novel Materials for Information Technology of Zhejiang Province, Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University, Hangzhou 310027 (China); Ferroic Physics Group, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Hu, Shanshan; Bai, Guohua; Yan, Mi; Lu, Yunhao, E-mail: luyh@zju.edu.cn [State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Key Laboratory of Novel Materials for Information Technology of Zhejiang Province, Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University, Hangzhou 310027 (China); Li, Huiying [Multi-disciplinary Materials Research Center, Frontier Institute of Science and Technology, Xi' an Jiaotong University, Xi' an 710049 (China); Peng, Xiaoling [College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018 (China); Ren, Xiaobing [Ferroic Physics Group, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Multi-disciplinary Materials Research Center, Frontier Institute of Science and Technology, Xi' an Jiaotong University, Xi' an 710049 (China)
2015-03-16
Soluting rare earth atoms Tb or Dy into body centered cubic (BCC) Fe-Ga through rapid cooling significantly enhances the magnetostriction due to strong localized magnetocrystalline anisotropy. Origin of the local strong anisotropy, however, awaits comprehensive microstructural investigation. In this letter, formation of tetragonal nanoparticles with c/a ∼ 0.979 has been found in the giant magnetostrictive ribbons Fe{sub 82.89}Ga{sub 16.88}Tb{sub 0.23} due to local symmetry breaking of the BCC lattice using high resolution transmission electronic microscopy. First principal calculations suggest that random replacement of Tb atoms for Fe or Ga in the ordered DO{sub 3} superlattice is beneficial in the formation of such tetragonal symmetry. Exchange couplings between the nearest Tb-Fe or Tb-Tb pairs of the tetragonal nanoparticles might generate strong localized magnetocrystalline anisotropy, leading to extraordinary magnetostriction enhancement.
Anisotropy of the magnetoviscous effect in a cobalt ferrofluid with strong interparticle interaction
Energy Technology Data Exchange (ETDEWEB)
Linke, J.M., E-mail: julia.linke@tu-dresden.de; Odenbach, S.
2015-12-15
The anisotropy of the magnetoviscous effect (MVE) of a cobalt ferrofluid has been studied in a slit die viscometer for three orientations of the applied magnetic field: in the direction of the fluid flow (Δη{sub 1}), the velocity gradient (Δη{sub 2}), and the vorticity (Δη{sub 3}). The majority of the cobalt particles in the ferrofluid exhibit a strong dipole–dipole interaction, which corresponds to a weighted interaction parameter of λ{sub w}≈10.6. Thus the particles form extended microstructures inside the fluid which lead to enhanced MVE ratios Δη{sub 2}/Δη{sub 1}>3 and Δη{sub 3}/Δη{sub 1}>0.3 even for strong shearing and weak magnetic fields compared to fluids which contain non-interacting spherical particles with Δη{sub 2}/Δη{sub 1}≈1 and Δη{sub 3}/Δη{sub 1}=0. Furthermore, a non-monotonic increase has been observed in the shear thinning behavior of Δη{sub 2} for weak magnetic fields <10 kA/m, which cannot be explained solely by the magnetization of individual particles and the formation and disintegration of linear particle chains but indicates the presence of heterophase structures. - Highlights: • The magnetoviscous effect in a ferrofluid with strong interaction is anisotropic. • The strongest effects are found in a magnetic field parallel to the shear gradient. • In strong magnetic fields the microstructure of the fluid is stable against shearing. • In weak fields the fluid behavior indicates the presence of heterophase structures.
Strongly nonlinear dynamics of electrolytes in large ac voltages
Olesen, Laurits H; Bruus, Henrik
2009-01-01
We study the response of a model micro-electrochemical cell to a large ac voltage of frequency comparable to the inverse cell relaxation time. To bring out the basic physics, we consider the simplest possible model of a symmetric binary electrolyte confined between parallel-plate blocking electrodes, ignoring any transverse instability or fluid flow. We analyze the resulting one-dimensional problem by matched asymptotic expansions in the limit of thin double layers and extend previous work into the strongly nonlinear regime, which is characterized by two novel features - significant salt depletion in the electrolyte near the electrodes and, at very large voltage, the breakdown of the quasi-equilibrium structure of the double layers. The former leads to the prediction of "ac capacitive desalination", since there is a time-averaged transfer of salt from the bulk to the double layers, via oscillating diffusion layers. The latter is associated with transient diffusion limitation, which drives the formation and co...
Ensemble-based Kalman Filters in Strongly Nonlinear Dynamics
Institute of Scientific and Technical Information of China (English)
Zhaoxia PU; Joshua HACKER
2009-01-01
This study examines the effectiveness of ensemble Kalman filters in data assimilation with the strongly nonlinear dynamics of the Lorenz-63 model, and in particular their use in predicting the regime transition that occurs when the model jumps from one basin of attraction to the other. Four configurations of the ensemble-based Kalman filtering data assimilation techniques, including the ensemble Kalman filter, ensemble adjustment Kalman filter, ensemble square root filter and ensemble transform Kalman filter, are evaluated with their ability in predicting the regime transition (also called phase transition) and also are compared in terms of their sensitivity to both observational and sampling errors. The sensitivity of each ensemble-based filter to the size of the ensemble is also examined.
Modeling Plasmas with Strong Anisotropy, Neutral Fluid Effects, and Open Boundaries
Meier, Eric T.
Three computational plasma science topics are addressed in this research: the challenge of modeling strongly anisotropic thermal conduction, capturing neutral fluid effects in collisional plasmas, and modeling open boundaries in dissipative plasmas. The research efforts on these three topics contribute to a common objective: the improvement and extension of existing magnetohydrodynamic modeling capability. Modeling magnetically confined fusion-related plasmas is the focus of the research, but broader relevance is recognized and discussed. Code development is central to this work, and has been carried out within the flexible physics framework of the highly parallel HiFi implicit spectral element code. In magnetic plasma confinement, heat conduction perpendicular to the magnetic field is extremely slow compared to conduction parallel to the field. The anisotropy in heat conduction can be many orders of magnitude, and the inaccuracy of low-order representations can allow parallel heat transport to "leak" into the perpendicular direction, resulting in numerical perpendicular transport. If the computational grid is aligned to the magnetic field, this numerical error can be eliminated, even for low-order representations. However, grid alignment is possible only in idealized problems. In realistic applications, magnetic topology is chaotic. A general approach for accurately modeling the extreme anisotropy of fusion plasmas is to use high-order representations which do not require grid alignment for sufficient resolution. This research provides a comprehensive assessment of spectral element representation of anisotropy, in terms of dependence of accuracy on grid alignment, polynomial degree, and grid cell size, and gives results for two- and three-dimensional cases. Truncating large physical domains to concentrate computational resources is often necessary or desirable in simulating natural and man-made plasmas. A novel open boundary condition (BC) treatment for such
Nonlinear neutrino-photon interactions inside strong laser pulses
Meuren, Sebastian; Di Piazza, Antonino
2015-01-01
Even though neutrinos are neutral particles and interact only via the exchange of weak gauge bosons, charged leptons and quarks can mediate a coupling to the photon field beyond tree level. Inside a relativistically strong laser field nonlinear effects in the laser amplitude can play an important role, as electrons and positrons interact nonperturbatively with the coherent part of the photon field. Here, we calculate for the first time the leading-order contribution to the axial-vector--vector current-coupling tensor inside an arbitrary plane-wave laser field (which is taken into account exactly by employing the Furry picture). The current-coupling tensor appears in the calculation of various electroweak processes inside strong laser fields like photon emission or trident electron-positron pair production by a neutrino. Moreover, as we will see below, the axial-vector--vector current-coupling tensor contains the Adler-Bell-Jackiw (ABJ) anomaly. This occurrence renders the current-coupling tensor also interest...
Nonlinear Debye screening in strongly-coupled plasmas
Sarmah, D; Tessarotto, M
2006-01-01
An ubiquitous property of plasmas is the so-called Debye shielding of the electrostatic potential. Important aspects of Debye screening concern, in particular, the investigation of non-linear charge screening effects taking place in strongly-coupled plasmas, that imply a reduction of the effective charge characterizing the Debye-H\\"{u}ckel potential. These effects are particularly relevant in dusty plasmas which are characterized by high-Z particles. The investigation of the effective interactions of these particles has attracted interest in recent years especially for numerical simulations. In this work we intend to analyze the consistency of the traditional mathematical model for the Debye screening. In particular, we intend to prove that the 3D Poisson equation involved in the DH model does not admit strong solutions. For this purpose a modified model is proposed which takes into account the effect of local plasma sheath (i.e., the local domain near test particles where the plasma must be considered discre...
Strong nonlinear harmonic generation in a PZT/Aluminum resonator
Energy Technology Data Exchange (ETDEWEB)
Parenthoine, D; Haumesser, L; Meulen, F Vander; Tran-Huu-Hue, L-P, E-mail: parenthoine@univ-tours.f [University Francois Rabelais of Tours, U 930 Imagerie et Cerveau, CNRS 2448, ENIVL, rue de la Chocolaterie, BP 3410, 41034 Blois (France)
2009-11-01
In this work, the extentional vibration mode of a coupled PZT/ Aluminum rod resonator is studied experimentally. Geometrical characteristics of the PZT are its 27 mm length and its 4x4 mm{sup 2} cross section area. The excitation voltage consists in sinusoidal bursts in the frequency range (20-80 kHz). Velocity measurements are performed at both ends of this system, using a laser probe. Strong harmonic distortions in the mechanical response (up to -20 dB with respect to the primary wave amplitude) have been observed. The corresponding input levels are far lower than those which are necessary to observe quadratic second harmonic generation in a free PZT resonator. The strong nonlinear effect can be explained as a super-harmonic resonance of the system due to a specific ratio between the eigen frequencies of the two parts of the resonator. Evolution of fundamental and harmonic responses are observed as a function of input levels, highlighting hysteretic behavior.
Simulation of facet dendrite growth with strong interfacial energy anisotropy by phase field method
Institute of Scientific and Technical Information of China (English)
袁训锋; 刘宝盈; 李春; 周春生; 丁雨田
2015-01-01
Numerical simulations based on a new regularized phase-field model were presented, to simulate the solidification of hexagonal close-packed materials with strong interfacial energy anisotropies. Results show that the crystal grows into facet dendrites, displaying six-fold symmetry. The size of initial crystals has an effect on the branching-off of the principal branch tip along the direction, which is eliminated by setting the b/a (a and b are the semi-major and semi-minor sizes in the initial elliptical crystals, respectively) value to be less than or equal to 1. With an increase in the undercooling value, the equilibrium morphology of the crystal changes from a star-like shape to facet dendrites without side branches. The steady-state tip velocity increases exponentially when the dimensionless undercooling is below the critical value. With a further increase in the undercooling value, the equilibrium morphology of the crystal grows into a developed side-branch structure, and the steady-state tip velocity of the facet dendrites increases linearly. The facet dendrite growth has controlled diffusion and kinetics.
The Behavior of Filters and Smoothers for Strongly Nonlinear Dynamics
Zhu, Yanqiu; Cohn, Stephen E.; Todling, Ricardo
1999-01-01
The Kalman filter is the optimal filter in the presence of known Gaussian error statistics and linear dynamics. Filter extension to nonlinear dynamics is non trivial in the sense of appropriately representing high order moments of the statistics. Monte Carlo, ensemble-based, methods have been advocated as the methodology for representing high order moments without any questionable closure assumptions (e.g., Miller 1994). Investigation along these lines has been conducted for highly idealized dynamics such as the strongly nonlinear Lorenz (1963) model as well as more realistic models of the oceans (Evensen and van Leeuwen 1996) and atmosphere (Houtekamer and Mitchell 1998). A few relevant issues in this context are related to the necessary number of ensemble members to properly represent the error statistics and, the necessary modifications in the usual filter equations to allow for correct update of the ensemble members (Burgers 1998). The ensemble technique has also been applied to the problem of smoothing for which similar questions apply. Ensemble smoother examples, however, seem to quite puzzling in that results of state estimate are worse than for their filter analogue (Evensen 1997). In this study, we use concepts in probability theory to revisit the ensemble methodology for filtering and smoothing in data assimilation. We use Lorenz (1963) model to test and compare the behavior of a variety implementations of ensemble filters. We also implement ensemble smoothers that are able to perform better than their filter counterparts. A discussion of feasibility of these techniques to large data assimilation problems will be given at the time of the conference.
Kandpal, Lalit M.; Singh, Sandeep; Kumar, Pawan; Siwach, P. K.; Gupta, Anurag; Awana, V. P. S.; Singh, H. K.
2016-06-01
The present study reports the impact of magnetic anisotropy (MA) on magnetotransport properties such as the magnetic transitions, magnetic liquid behavior, glass transition and anisotropic magnetoresistance (AMR) in epitaxial film (thickness 42 nm) of strongly phase separated manganite La5/8-yPryCa3/8MnO3 (y≈0.4). Angle dependent magnetization measurement confirms the out-of-plane magnetic anisotropy with the magnetic easy axes aligned in the plane of the film and the magnetic hard axis along the normal to the film plane. The more prominent divergence between the zero filed cooled (ZFC) and field cooled warming (FCW) and the stronger hysteresis between the field cooled cooling (FCC) and FCW magnetization for H ∥ shows the weakening of the magnetic liquid along the magnetic hard axis. The peak at Tp≈42 K in FCW magnetization, which characterizes the onset of spin freezing shifts down to Tp≈18 K as the field direction is switched from the easy axes (H ∥) to the hard axis (H ⊥). The glass transition, which appears at Tg≈28 K for H ∥ disappears for H ⊥. The easy axis magnetization (M∣∣) appears to saturate around H~20 kOe, but the hard axis counterpart (M⊥) does not show such tendency even up to H=50 kOe. MA appears well above the ferromagnetic (FM) transition at T≈170 K, which is nearly the same as the Neel temperature (TN) of M⊥ - T . The temperature dependent resistivity measured at H=10 kOe applied along the easy axis (ρ|| - T) and the hard axis (ρ⊥ - T) shows insulator metal transition (IMT) at ≈106 K and ≈99 K in the cooling cycle, respectively. The large difference between ρ⊥ - T and ρ|| - T during the cooling cycle and in the vicinity of IMT results in huge AMR of ≈-142% and -115%. The observed properties have been explained in terms of the MA induced variation in the relative fraction of the coexisting magnetic phases.
Nonlinear evolution of cosmic magnetic fields and cosmic microwave background anisotropies
Tashiro, Hiroyuki; Sugiyama, Naoshi; Banerjee, Robi
2006-01-01
In this work we investigate the effects of primordial magnetic fields on cosmic microwave background anisotropies (CMB). Based on cosmological magneto-hydro dynamic (MHD) simulations [R. Banerjee and K. Jedamzik, Phys. Rev. DPRVDAQ0556-2821 70, 123003 (2004).10.1103/PhysRevD.70.123003] we calculate the CMB anisotropy spectra and polarization induced by fluid fluctuations (Alfvén modes) generated by primordial magnetic fields. The strongest effect on the CMB spectra comes from the transition epoch from a turbulent regime to a viscous regime. The balance between magnetic and kinetic energy until the onset of the viscous regime provides a one to one relation between the comoving coherence length L and the comoving magnetic field strength B, such as L˜30(B/10-9Gauss)3pc. The resulting CMB temperature and polarization anisotropies for the initial power law index of the magnetic fields n>3/2 are somewhat different from the ones previously obtained by using linear perturbation theory. In particular, differences can appear on intermediate scales l20000. On scales l0.7Mpc for the most extreme case, or B0.8Mpc for the most conservative case. We may also expect higher signals on large scales of the polarization spectra compared to linear calculations. The signal may even exceed the B-mode polarization from gravitational lensing depending on the strength of the primordial magnetic fields. On very small scales, the diffusion damping scale of nonlinear calculations turns out to be much smaller than the one of linear calculations if the comoving magnetic field strength B>16nGauss. If the magnetic field strength is smaller, the diffusion scales become smaller too. Therefore we expect to have both, temperature and polarization anisotropies, even beyond l>10000 regardless of the strength of the magnetic fields. The peak values of the temperature anisotropy and the B-mode polarization spectra are approximately 40μK and a few μK, respectively.
Strong out-of-plane magnetic anisotropy in ion irradiated anatase TiO2 thin films
Directory of Open Access Journals (Sweden)
M. Stiller
2016-12-01
Full Text Available The temperature and field dependence of the magnetization of epitaxial, undoped anatase TiO2 thin films on SrTiO3 substrates was investigated. Low-energy ion irradiation was used to modify the surface of the films within a few nanometers, yet with high enough energy to produce oxygen and titanium vacancies. The as-prepared thin film shows ferromagnetism which increases after irradiation with low-energy ions. An optimal and clear magnetic anisotropy was observed after the first irradiation, opposite to the expected form anisotropy. Taking into account the experimental parameters, titanium vacancies as di-Frenkel pairs appear to be responsible for the enhanced ferromagnetism and the strong anisotropy observed in our films. The magnetic impurities concentrations was measured by particle-induced X-ray emission with ppm resolution. They are ruled out as a source of the observed ferromagnetism before and after irradiation.
Nonlinear quantum electrodynamic and electroweak processes in strong laser fields
Energy Technology Data Exchange (ETDEWEB)
Meuren, Sebastian
2015-06-24
Various nonlinear electrodynamic and electroweak processes in strong plane-wave laser fields are considered with an emphasis on short-pulse effects. In particular, the momentum distribution of photoproduced electron-positron pairs is calculated numerically and a semiclassical interpretation of its characteristic features is established. By proving the optical theorem, compact double-integral expressions for the total pair-creation probability are obtained and numerically evaluated. The exponential decay of the photon wave function in a plane wave is included by solving the Schwinger-Dyson equations to leading-order in the quasistatic approximation. In this respect, the polarization operator in a plane wave is investigated and its Ward-Takahashi identity verified. A classical analysis indicates that a photoproduced electron-positron pair recollides for certain initial conditions. The contributions of such recollision processes to the polarization operator are identified and calculated both analytically and numerically. Furthermore, the existence of nontrivial electron-spin dynamics induced by quantum fluctuations is verified for ultra-short laser pulses. Finally, the exchange of weak gauge bosons is considered, which is essential for neutrino-photon interactions. In particular, the axial-vector-vector coupling tensor is calculated and the so-called Adler-Bell-Jackiw (ABJ) anomaly investigated.
Nonlinear turbulence models for predicting strong curvature effects
Institute of Scientific and Technical Information of China (English)
XU Jing-lei; MA Hui-yang; HUANG Yu-ning
2008-01-01
Prediction of the characteristics of turbulent flows with strong streamline curvature, such as flows in turbomachines, curved channel flows, flows around airfoils and buildings, is of great importance in engineering applicatious and poses a very practical challenge for turbulence modeling. In this paper, we analyze qualitatively the curvature effects on the structure of turbulence and conduct numerical simulations of a turbulent U- duct flow with a number of turbulence models in order to assess their overall performance. The models evaluated in this work are some typical linear eddy viscosity turbulence models, nonlinear eddy viscosity turbulence models (NLEVM) (quadratic and cubic), a quadratic explicit algebraic stress model (EASM) and a Reynolds stress model (RSM) developed based on the second-moment closure. Our numerical results show that a cubic NLEVM that performs considerably well in other benchmark turbulent flows, such as the Craft, Launder and Suga model and the Huang and Ma model, is able to capture the major features of the highly curved turbulent U-duct flow, including the damping of turbulence near the convex wall, the enhancement of turbulence near the concave wall, and the subsequent turbulent flow separation. The predictions of the cubic models are quite close to that of the RSM, in relatively good agreement with the experimental data, which suggests that these inodels may be employed to simulate the turbulent curved flows in engineering applications.
DEFF Research Database (Denmark)
Enemark, Søren; Santos, Ilmar F.
2016-01-01
In this work, the nonlinear dynamic behaviour of a vertical rigid rotor interacting with a flexible foundation by means of two passive magnetic bearings is quantified and evaluated. The quantification is based on theoretical and experimental investigation of the non-uniformity (anisotropy) of the...
Quantum nonlinear optics with single photons enabled by strongly interacting atoms
DEFF Research Database (Denmark)
Peyronel, Thibault; Firstenberg, Ofer; Liang, Qi Yu
2012-01-01
The realization of strong nonlinear interactions between individual light quanta (photons) is a long-standing goal in optical science and engineering, being of both fundamental and technological significance. In conventional optical materials, the nonlinearity at light powers corresponding...
Measurement-Induced Strong Kerr Nonlinearity for Weak Quantum States of Light
Costanzo, Luca S.; Coelho, Antonio S.; Biagi, Nicola; Fiurášek, Jaromír; Bellini, Marco; Zavatta, Alessandro
2017-07-01
Strong nonlinearity at the single photon level represents a crucial enabling tool for optical quantum technologies. Here we report on experimental implementation of a strong Kerr nonlinearity by measurement-induced quantum operations on weak quantum states of light. Our scheme coherently combines two sequences of single photon addition and subtraction to induce a nonlinear phase shift at the single photon level. We probe the induced nonlinearity with weak coherent states and characterize the output non-Gaussian states with quantum state tomography. The strong nonlinearity is clearly witnessed as a change of sign of specific off-diagonal density matrix elements in the Fock basis.
Huang, Chun-Yuh; Stankiewicz, Anna; Ateshian, Gerard A; Mow, Van C
2005-04-01
The tensile and compressive properties of human glenohumeral cartilage were determined by testing 120 rectangular strips in uniaxial tension and 70 cylindrical plugs in confined compression, obtained from five human glenohumeral joints. Specimens were harvested from five regions across the articular surface of the humeral head and two regions on the glenoid. Tensile strips were obtained along two orientations, parallel and perpendicular to the split-line directions. Two serial slices through the thickness, corresponding to the superficial and middle zones of the cartilage layers, were prepared from each tensile strip and each compressive plug. The equilibrium tensile modulus and compressive aggregate modulus of cartilage were determined from the uniaxial tensile and confined compression tests, respectively. Significant differences in the tensile moduli were found with depth and orientation relative to the local split-line direction. Articular cartilage of the humeral head was significantly stiffer in tension than that of the glenoid. There were significant differences in the aggregate compressive moduli of articular cartilage between superficial and middle zones in the humeral head. Furthermore, tensile and compressive stress-strain responses exhibited nonlinearity under finite strain, while the tensile modulus differed by up to two orders of magnitude from the compressive aggregate modulus at 0% strain, demonstrating a high degree of tension-compression nonlinearity. The complexity of the mechanical properties of human glenohumeral cartilage was exposed in this study, showing anisotropy, inhomogeneity, and tension-compression nonlinearity within the same joint. The observed differences in the tensile properties of human glenohumeral cartilage suggest that the glenoid may be more susceptible to cartilage degeneration than the humeral head.
An Analytical Approximation Method for Strongly Nonlinear Oscillators
Directory of Open Access Journals (Sweden)
Wang Shimin
2012-01-01
Full Text Available An analytical method is proposed to get the amplitude-frequency and the phase-frequency characteristics of free/forced oscillators with nonlinear restoring force. The nonlinear restoring force is expressed as a spring with varying stiffness that depends on the vibration amplitude. That is, for stationary vibration, the restoring force linearly depends on the displacement, but the stiffness of the spring varies with the vibration amplitude for nonstationary oscillations. The varied stiffness is constructed by means of the first and second averaged derivatives of the restoring force with respect to the displacement. Then, this stiffness gives the amplitude frequency and the phase frequency characteristics of the oscillator. Various examples show that this method can be applied extensively to oscillators with nonlinear restoring force, and that the solving process is extremely simple.
Strong nonlinear photonic responses from microbiologically synthesized tellurium nanocomposites
Liao, K.-S.; Wang, Jingyuan; Dias, S.; Dewald, J.; Alley, N.J.; Baesman, S.M.; Oremland, R.S.; Blau, W.J.; Curran, S.A.
2010-01-01
A new class of nanomaterials, namely microbiologically-formed nanorods composed of elemental tellurium [Te(0)] that forms unusual nanocomposites when combined with poly(m-phenylenevinylene-co-2,5-dioctoxy-phenylenevinylene) (PmPV) is described. These bio-nanocomposites exhibit excellent broadband optical limiting at 532 and 1064 nm. Nonlinear scattering, originating from the laser induced solvent bubbles and microplasmas, is responsible for this nonlinear behavior. The use of bacterially-formed Te(0) when combined with an organic chemical host (e.g., PmPV) is a new green method of nanoparticle syntheses. This opens the possibilities of using unique, biologically synthesized materials to advance future nanoelectronic and nanophotonic applications. ?? 2009 Elsevier B.V. All rights reserved.
Nonlinear processes in the strong wave-plasma interaction
Pegoraro, Francesco; Califano, Francesco; Attico, Nicola; Bulanov, Sergei
2000-10-01
Nonlinear interactions in hot laboratory and/or astrophysical plasmas are a very efficient mechanism able to transfer the energy from the large to the small spatial scales of the system. As a result, kinetic processes are excited and play a key role in the plasma dynamics since the typical fluid dissipative length scales (where the nonlinear cascade is stopped) are (much) smaller then the kinetic length scales. Then, the key point is the role of the kinetic effects in the global plasma dynamics, i.e. whether the kinetic effects remains confined to the small scales of the system or whether there is a significant feedback on the large scales. Here we will address this problem by discussing the nonlinear kinetic evolution of the electromagnetic beam plasma instability where phase space vortices, as well as large scale vortex like magnetic structures in the physical space, are generated by wave - particle interactions. The role and influence of kinetic effects on the large scale plasma dynamics will be also discussed by addressing the problem of collisionless magnetic reconection.
Strong perpendicular magnetic anisotropy in [Co/Pt] n ultrathin superlattices
Liu, Yi; Qiu, Jinjun; Ter Lim, Sze; Li Toh, Suey; Zhu, Zhengyong; Han, Guchang; Zhu, Kaigui
2017-01-01
Ultrathin [Co/Pt] n superlattice films consisting of 0.18-0.60-nm-thick Co and Pt sublayers were deposited by sputtering. A large in-plane saturation field (H s) of ˜39 kOe and a very large effective perpendicular magnetic anisotropy (K eff) with a magnitude of 107 erg/cm3 were attained. The highest K eff was ˜1.40 × 107 erg/cm3. These films are promising candidates for the reference layer of the p-MgO magnetic tunnel junction in Gb-scale magnetic random-access memory.
Elegant Ince-Gaussian breathers in strongly nonlocal nonlinear media
Institute of Scientific and Technical Information of China (English)
Bai Zhi-Yong; Deng Dong-Mei; Guo Qi
2012-01-01
A novel class of optical breathers,called elegant Ince-Gaussian breathers,are presented in this paper.They are exact analytical solutions to Snyder and Mitchell's mode in an elliptic coordinate system,and their transverse structures are described by Ince-polynomials with complex arguments and a Gaussian function.We provide convincing evidence for the correctness of the solutions and the existence of the breathers via comparing the analytical solutions with numerical simulation of the nonlocal nonlinear Schr(o)dinger equation.
NMR analysis of an Fe(i)-carbene complex with strong magnetic anisotropy.
Damjanović, Marko; Samuel, Prinson P; Roesky, Herbert W; Enders, Markus
2017-04-19
A tricoordinated Fe(I) complex with two cyclic-alkyl(amino) carbene (cAAC) and one chlorido ligand, (cAAC)2FeCl (1), is studied by means of (1)H NMR spectroscopy and DFT calculations. Due to the cAAC ligands, which can take significant amounts of spin density from the metal center, and due to the magnetic anisotropy of the Fe(I) ion (P. P. Samuel et al., J. Am. Chem. Soc., 2014, 136, 11964-11971), compound 1 is a rare example of a paramagnetic d-block compound which is expected to have significant contributions from both contact and pseudocontact terms to the hyperfine NMR shift. Compound 1 is fluxional, which makes the analysis of its (1)H NMR spectrum more difficult but allows a preliminary assignment from EXSY spectra. Then, a software-aided approach enabled a satisfactory signal assignment of all protons which are distanced from the Fe(I) center and carbene cyclic core, and thereby the extraction of the axial and rhombic components of the magnetic susceptibility anisotropy tensor (Δχ). Components of Δχ enable the calculation of zero-field spitting D and E parameters from solution NMR measurements of 1, and these parameters are compared to previously reported experimental and theoretical values.
Indian Academy of Sciences (India)
Tulika Gupta; Gopalan Rajaraman
2014-09-01
Ab initio CASSCF+RASSI-SO investigations on a series of lanthanide complexes [LnIII = Dy(1), Tb(2), Ce(3), Nd(4), Pr(5) and Sm(6)] have been undertaken and in selected cases (for 1, 2, 3 and 4) coordination number (C.N.) around the LnIII ion has been gradually varied to ascertain the effect of C.N. on the magnetic anisotropy. Our calculations reveal that complex 3 possesses the highest barrier height for reorientation of magnetisation (Ueff) and predict that 3 is likely to exhibit Single Molecule Magnet (SMM) behaviour. Complex 5 on the other hand is predicted to preclude any SMM behaviour as there is no intrinsic barrier for reorientation of magnetization. Ground state anisotropy of all the complexes show mixed behaviour ranging from pure Ising type to fully rhombic behaviour. Coordination number around the lanthanide ion is found to alter the magnetic behaviour of all the lanthanide complexes studied and this is contrary to the general belief that the lanthanide ions are inert and exert small ligand field interaction.High symmetric low-coordinate LnIII complexes are found to yield large Ueff values and thus should be the natural targets for achieving very large blocking temperatures.
Relativistic nonlinear electrodynamics the QED vacuum and matter in super-strong radiation fields
Avetissian, Hamlet K
2016-01-01
This revised edition of the author’s classic 2006 text offers a comprehensively updated review of the field of relativistic nonlinear electrodynamics. It explores the interaction of strong and super-strong electromagnetic/laser radiation with the electromagnetic quantum vacuum and diverse types of matter – including free charged particles and antiparticles, acceleration beams, plasma and plasmous media. The appearance of laser sources of relativistic and ultra-relativistic intensities over the last decade has stimulated investigation of a large class of processes under such super-strong radiation fields. Revisions for this second edition reflect these developments and the book includes new chapters on Bremsstrahlung and nonlinear absorption of superintense radiation in plasmas, the nonlinear interaction of relativistic atoms with intense laser radiation, nonlinear interaction of strong laser radiation with Graphene, and relativistic nonlinear phenomena in solid-plasma targets under supershort laser pul...
Strong Convergence of Modified Ishikawa Iterations for Nonlinear Mappings
Indian Academy of Sciences (India)
Yongfu Su; Xiaolong Qin
2007-02-01
In this paper, we prove a strong convergence theorem of modified Ishikawa iterations for relatively asymptotically nonexpansive mappings in Banach space. Our results extend and improve the recent results by Nakajo, Takahashi, Kim, $Xu$, Matsushita and some others.
Nonlinear Weibel Instability and Turbulence in Strong Collisionless Shocks
Energy Technology Data Exchange (ETDEWEB)
Medvedev, Mikhail M.
2008-08-31
This research project was devoted to studies of collisionless shocks, their properties, microphysics and plasma physics of underlying phenomena, such as Weibel instability and generation of small-scale fields at shocks, particle acceleration and transport in the generated random fields, radiation mechanisms from these fields in application to astrophysical phenomena and laboratory experiments (e.g., laser-plasma and beam-plasma interactions, the fast ignition and inertial confinement, etc.). Thus, this study is highly relevant to astrophysical sciences, the inertial confinement program and, in particular, the Fast Ignition concept, etc. It makes valuable contributions to the shock physics, nonlinear plasma theory, as well as to the basic plasma science, in general.
Noninvasive nonlinear imaging through strongly-scattering turbid layers
Katz, Ori; Guan, Yefeng; Silberberg, Yaron
2014-01-01
Diffraction-limited imaging through complex scattering media is a long sought after goal with important applications in biomedical research. In recent years, high resolution wavefront-shaping has emerged as a powerful approach to generate a sharp focus through highly scattering, visually opaque samples. However, it requires a localized feedback signal from the target point of interest, which necessitates an invasive procedure in all-optical techniques. Here, we show that by exploiting optical nonlinearities, a diffraction-limited focus can be formed inside or through a complex sample, even when the feedback signal is not localized. We prove our approach theoretically and numerically, and experimentally demonstrate it with a two-photon fluorescence signal through highly scattering biological samples. We use the formed focus to perform two-photon microscopy through highly scattering, visually opaque layers.
Strongly nonlinear dynamics of electrolytes in large ac voltages
DEFF Research Database (Denmark)
Olesen, Laurits Højgaard; Bazant, Martin Z.; Bruus, Henrik
2010-01-01
We study the response of a model microelectrochemical cell to a large ac voltage of frequency comparable to the inverse cell relaxation time. To bring out the basic physics, we consider the simplest possible model of a symmetric binary electrolyte confined between parallel-plate blocking electrodes...... in the electrolyte near the electrodes and, at very large voltage, the breakdown of the quasiequilibrium structure of the double layers. The former leads to the prediction of “ac capacitive desalination” since there is a time-averaged transfer of salt from the bulk to the double layers, via oscillating diffusion...... nonlinear responses to large ac voltages, such as Faradaic reactions, electro-osmotic instabilities, and induced-charge electrokinetic phenomena....
Poloidal rotation driven by nonlinear momentum transport in strong electrostatic turbulence
Wang, Lu; Wen, Tiliang; Diamond, P. H.
2016-10-01
Virtually, all existing theoretical works on turbulent poloidal momentum transport are based on quasilinear theory. Nonlinear poloidal momentum flux— is universally neglected. However, in the strong turbulence regime where relative fluctuation amplitude is no longer small, quasilinear theory is invalid. This is true at the all-important plasma edge. In this work, nonlinear poloidal momentum flux in strong electrostatic turbulence is calculated using the Hasegawa-Mima equation, and is compared with quasilinear poloidal Reynolds stress. A novel property is that symmetry breaking in fluctuation spectrum is not necessary for a nonlinear poloidal momentum flux. This is fundamentally different from the quasilinear Reynold stress. Furthermore, the comparison implies that the poloidal rotation drive from the radial gradient of nonlinear momentum flux is comparable to that from the quasilinear Reynolds force. Nonlinear poloidal momentum transport in strong electrostatic turbulence is thus not negligible for poloidal rotation drive, and so may be significant to transport barrier formation.
Strongly driven nonlinear quantum optics in microring resonators
Vernon, Z
2015-01-01
We present a detailed analysis of strongly driven spontaneous four-wave mixing in a lossy integrated microring resonator side-coupled to a channel waveguide. A nonperturbative, analytic solution within the undepleted pump approximation is developed for a cw pump input of arbitrary intensity. In the strongly driven regime self- and cross-phase modulation, as well as multi-pair generation, lead to a rich variety of power-dependent effects; the results are markedly different than in the low power limit. The photon pair generation rate, single photon spectrum, and joint spectral intensity (JSI) distribution are calculated. Splitting of the generated single photon spectrum into a doublet structure associated with both pump detuning and cross-phase modulation is predicted, as well as substantial narrowing of the generated signal and idler bandwidths associated with the onset of optical parametric oscillation at intermediate powers. Both the correlated and uncorrelated contributions to the JSI are calculated, and fo...
Asymptotic Behavior for a Strongly Damped Nonlinear Wave Equation.
1980-06-01
principle to reaction- diffusion equations, J. Differential Equations 33(1979), 201-225. [2] Billotti, J.E. and J.P. LaSalle , Periodic dissipative...results of Alikakos. Invariant sets in one space are automatically invariant sets in many spaces (which implies smoothness properties of invariant sets...of a "very smooth" maximal compact invariant set under a very weak dissipative assumption, along with its strong stability and attractivity properties
Exact Penalty Function and Asymptotic Strong Nonlinear Duality in Integer Programming
Institute of Scientific and Technical Information of China (English)
Fu-sheng Bai; Z.Y.Wu; L.S. Zhang
2004-01-01
In this paper, a logarithmic-exponential penalty function with two parameters for integer programmingis discussed. We obtain the exact penalty properties and then establish the asymptotic strong nonlinear duality in the corresponding logarithmic-exponential dual formulation by using the obtained exact penalty properties.The discussion is based on the logarithmic-exponential nonlinear dual formulation proposed in [6].
Nonlinear diffusion of a strong magnetic field in a conducting medium
Energy Technology Data Exchange (ETDEWEB)
Fedorov, V.F.
1985-09-01
The problem considered here is a self-similar problem concerning nonlinear diffusion of a strong magnetic field in a conducting nonmagnetic incompressible medium where the magnetic field is produced by a current passing along the symmetry axis. Nonlinear diffusion equations are solved analytically for various particular cases with allowance for the heating of the medium.
Gevrey Regularity for the Noncutoff Nonlinear Homogeneous Boltzmann Equation with Strong Singularity
Directory of Open Access Journals (Sweden)
Shi-you Lin
2014-01-01
Full Text Available The Cauchy problem of the nonlinear spatially homogeneous Boltzmann equation without angular cutoff is studied. By using analytic techniques, one proves the Gevrey regularity of the C∞ solutions in non-Maxwellian and strong singularity cases.
Directory of Open Access Journals (Sweden)
James Avery Sauls
2015-06-01
Full Text Available Recent theories of Sr2RuO4 based on the interplay of strong interactions, spin-orbit coupling and multi-band anisotropy predict chiral or helical ground states with strong anisotropy of the pairing states, with deep minima in the excitation gap, as well as strong phase anisotropy for the chiral ground state. We develop time-dependent mean field theory to calculate the Bosonic spectrum for the class of 2D chiral superconductors spanning 3He-A to chiral superconductors with strong anisotropy. Chiral superconductors support a pair of massive Bosonic excitations of the time-reversed pairs labeled by their parity under charge conjugation. These modes are degenerate for 2D 3He-A. Crystal field anisotropy lifts the degeneracy. Strong anisotropy also leads to low-lying Fermions, and thus to channels for the decay of the Bosonic modes. Selection rules and phase space considerations lead to large asymmetries in the lifetimes and hybridization of the Bosonic modes with the continuum of un-bound Fermion pairs. We also highlight results for the excitation of the Bosonic modes by microwave radiation that provide clear signatures of the Bosonic modes of an anisotropic chiral ground state.
Nonlinear properties of gated graphene in a strong electromagnetic field
Energy Technology Data Exchange (ETDEWEB)
Avetisyan, A. A., E-mail: artakav@ysu.am; Djotyan, A. P., E-mail: adjotyan@ysu.am [Yerevan State University, Department of Physics (Armenia); Moulopoulos, K., E-mail: cos@ucy.ac.cy [University of Cyprus, Department of Physics (Cyprus)
2017-03-15
We develop a microscopic theory of a strong electromagnetic field interaction with gated bilayer graphene. Quantum kinetic equations for density matrix are obtained using a tight binding approach within second quantized Hamiltonian in an intense laser field. We show that adiabatically changing the gate potentials with time may produce (at resonant photon energy) a full inversion of the electron population with high density between valence and conduction bands. In the linear regime, excitonic absorption of an electromagnetic radiation in a graphene monolayer with opened energy gap is also studied.
Thermally robust Mo/CoFeB/MgO trilayers with strong perpendicular magnetic anisotropy.
Liu, T; Zhang, Y; Cai, J W; Pan, H Y
2014-07-31
The recent discovery of perpendicular magnetic anisotropy (PMA) at the CoFeB/MgO interface has accelerated the development of next generation high-density non-volatile memories by utilizing perpendicular magnetic tunnel junctions (p-MTJs). However, the insufficient interfacial PMA in the typical Ta/CoFeB/MgO system will not only complicate the p-MTJ optimization, but also limit the device density scalability. Moreover, the rapid decreases of PMA in Ta/CoFeB/MgO films with annealing temperature higher than 300°C will make the compatibility with CMOS integrated circuits a big problem. By replacing the Ta buffer layer with a thin Mo film, we have increased the PMA in the Ta/CoFeB/MgO structure by 20%. More importantly, the thermal stability of the perpendicularly magnetized (001)CoFeB/MgO films is greatly increased from 300°C to 425°C, making the Mo/CoFeB/MgO films attractive for a practical p-MTJ application.
Institute of Scientific and Technical Information of China (English)
2008-01-01
In this article, we consider the existence of local and global solution to the Cauchy problem of a doubly nonlinear equation. By introducing the norms |||f|||h and
Strong anisotropy and magnetostriction in the two-dimensional Stoner ferromagnet Fe3GeTe2
Zhuang, Houlong L.; Kent, P. R. C.; Hennig, Richard G.
2016-04-01
Computationally characterizing magnetic properies of novel two-dimensional (2D) materials serves as an important first step of exploring possible applications. Using density-functional theory, we show that single-layer Fe3GeTe2 is a potential 2D material with sufficiently low formation energy to be synthesized by mechanical exfoliation from the bulk phase with a van der Waals layered structure. In addition, we calculated the phonon dispersion demonstrating that single-layer Fe3GeTe2 is dynamically stable. Furthermore, we find that similar to the bulk phase, 2D Fe3GeTe2 exhibits a magnetic moment that originates from a Stoner instability. In contrast to other 2D materials, we find that single-layer Fe3GeTe2 exhibits a significant uniaxial magnetocrystalline anisotropy energy of 920 μ eV per Fe atom originating from spin-orbit coupling. Finally, we show that applying biaxial tensile strains enhances the anisotropy energy, which reveals strong magnetostriction in single-layer Fe3GeTe2 with a sizable magneostrictive coefficient. Our results indicate that single-layer Fe3GeTe2 is potentially useful for magnetic storage applications.
Institute of Scientific and Technical Information of China (English)
NIU Jia-Sheng; MA Ben-Kun
2003-01-01
In this paper, we theoretically discuss the soliton properties of light pulse transportation on the surface of an ionic crystal having strong nonlinear interactions between ions of unit cells. We analyze in detail the dark solitons when the nonlinear coefficient g is positive and negative, respectively. It is found that whether the nonlinear coefficient g is positive or negative, the dark solitons can be formed over the whole dispersion relation area of surface polaritons considering nonlinear effects. Attention should be paid to the fact that around ωTO, the light pulse can form advanced dark solitons, and there is a switching area from advanced dark soliton to retarded dark soliton near ωTO. We also discuss the effects of higher nonlinear dispersion on the solitons.
Poloidal rotation driven by nonlinear momentum transport in strong electrostatic turbulence
Wang, Lu; Diamond, P H
2016-01-01
Virtually, all existing theoretical works on turbulent poloidal momentum transport are based on quasilinear theory. Nonlinear poloidal momentum flux - $\\langle \\tilde{v}_r \\tilde{n} \\tilde{v}_{\\theta} \\rangle$ is universally neglected. However, in the strong turbulence regime where relative fluctuation amplitude is no longer small, quasilinear theory is invalid. This is true at the all-important plasma edge. In this work, nonlinear poloidal momentum flux $ \\langle \\tilde{v}_r \\tilde{n} \\tilde{v}_{\\theta} \\rangle $ in strong electrostatic turbulence is calculated using Hasegawa-Mima equation, and is compared with quasilinear poloidal Reynolds stress. A novel property is that symmetry breaking in fluctuation spectrum is not necessary for a nonlinear poloidal momentum flux. This is fundamentally different from the quasilinear Reynold stress. Furthermore, the comparison implies that the poloidal rotation drive from the radial gradient of nonlinear momentum flux is comparable to that from the quasilinear Reynolds ...
Protogenov, A P
2001-01-01
The brief review of events, conditioned by the nonlinear modes strong correlations in the planar systems is presented. The analysis is limited by the Schroedinger nonlinear equation model. The fields stationary distributions are determined. The dependence of the particles number on the parameter characterizing the degree of looking, of the universal oscillation lines, is obtained. It is shown that by small values of this parameter there exists on the two-dimensional lattice the universal gravitation, which may be the dynamic cause of transition to the coherent state. The connection of the chiral nonlinear boundary modes with the violations of the Galilean-invariance of the considered system is discussed
DEFF Research Database (Denmark)
Lazarov, Boyan Stefanov; Thomsen, Jon Juel; Snaeland, Sveinn Orri
2008-01-01
The aim of this article is to investigate how highfrequency (HF) excitation, combined with strong nonlinear elastic material behavior, influences the effective material or structural properties for low-frequency excitation and wave propagation. The HF effects are demonstrated on discrete linear s...... spring-mass chains with non-linear inclusions. The presented analytical and numerical results suggest that the effective material properties can easily be altered by establishing finite amplitude HF standing waves in the non-linear regions of the chain....
Scaling and anisotropy in magnetohydrodynamic turbulence in a strong mean magnetic field.
Grappin, Roland; Müller, Wolf-Christian
2010-08-01
We present an analysis of the anisotropic spectral energy distribution in incompressible magnetohydrodynamic turbulence permeated by a strong mean magnetic field. The turbulent flow is generated by high-resolution pseudospectral direct numerical simulations with large-scale isotropic forcing. Examining the radial energy distribution for various angles θ with respect to B0 reveals a specific structure which remains hidden when not taking axial symmetry with respect to B0 into account. For each direction, starting at the forced large scales, the spectrum first exhibits an amplitude drop around a wave number k0 which marks the start of a scaling range and goes on up to a dissipative wave number k(d)(θ). The three-dimensional spectrum for k≥k0 is described by a single θ-independent functional form F(k/k(d)), with the scaling law being the same in every direction. The previous properties still hold when increasing the mean field from B0=5 up to B0=10b(rms), as well as when passing from resistive to ideal flows. We conjecture that at fixed B0 the direction-independent scaling regime is reached when increasing the Reynolds number above a threshold which raises with increasing B0. Below that threshold critically balanced turbulence is expected.
New approximate solutions for the strongly nonlinear cubic-quintic duffing oscillators
Karahan, M. M. Fatih; Pakdemirli, Mehmet
2016-06-01
Strongly nonlinear cubic-quintic Duffing oscillator is considered. Approximate solutions are derived using the multiple scales Lindstedt Poincare method (MSLP), a relatively new method developed for strongly nonlinear oscillators. The free undamped oscillator is considered first. Approximate analytical solutions of the MSLP are contrasted with the classical multiple scales (MS) method and numerical simulations. It is found that contrary to the classical MS method, the MSLP can provide acceptable solutions for the case of strong nonlinearities. Next, the forced and damped case is treated. Frequency response curves of both the MS and MSLP methods are obtained and contrasted with the numerical solutions. The MSLP method and numerical simulations are in good agreement while there are discrepancies between the MS and numerical solutions.
Free and Forced Vibrations of the Strongly Nonlinear Cubic-Quintic Duffing Oscillators
Karahan, M. M. Fatih; Pakdemirli, Mehmet
2017-01-01
Strongly nonlinear cubic-quintic Duffing oscillatoris considered. Approximate solutions are derived using the multiple scales Lindstedt Poincare method (MSLP), a relatively new method developed for strongly nonlinear oscillators. The free undamped oscillator is considered first. Approximate analytical solutions of the MSLP are contrasted with the classical multiple scales (MS) method and numerical simulations. It is found that contrary to the classical MS method, the MSLP can provide acceptable solutions for the case of strong nonlinearities. Next, the forced and damped case is treated. Frequency response curves of both the MS and MSLP methods are obtained and contrasted with the numerical solutions. The MSLP method and numerical simulations are in good agreement while there are discrepancies between the MS and numerical solutions.
Indian Academy of Sciences (India)
B P Panda; N C Mohapatra
2002-01-01
Compton proﬁles of momentum distribution of conduction electrons in the orthorhombic phase of -Ga metal at low temperature are calculated in the band model for the three crystallographic directions (100), (010), and (001). Unlike the results at room temperature, previously reported by Lengeler, Lasser and Mair, the present results show strong anisotropy in the Compton proﬁles with the momentum distribution along (001) direction being substantially different from the other two directions. While experimental data on Compton proﬁles at low temperatures are not available for comparison with theory, the resistivity data in -Ga at low temperature strongly support this anisotropic behaviour. Besides, the electronic heat capacity constant available from both experiment and present calculation suggests that the conduction electron distribution at low temperature in the orthorhombic phase is markedly different from the free-electron-like-distribution at room temperature, thus lending additional support to anisotropic behaviour of Compton proﬁles. It would be nice to have Compton proﬁles data from experiment at low temperature for direct comparison with theory. It is hoped that the present work would stimulate enough interest in that direction.
Directory of Open Access Journals (Sweden)
Jianping Cai
2003-01-01
Full Text Available A method of approximate potential is presented for the study of certain kinds of strongly nonlinear oscillators. This method is to express the potential for an oscillatory system by a polynomial of degree four such that the leading approximation may be derived in terms of elliptic functions. The advantage of present method is that it is valid for relatively large oscillations. As an application, the elapsed time of periodic motion of a strongly nonlinear oscillator with slowly varying parameters is studied in detail. Comparisons are made with other methods to assess the accuracy of the present method.
A note on a strongly damped wave equation with fast growing nonlinearities
2015-01-01
A note on a strongly damped wave equation with fast growing nonlinearities Varga Kalantarov and Sergey Zelik Citation: Journal of Mathematical Physics 56, 011501 (2015); doi: 10.1063/1.4905234 View online: http://dx.doi.org/10.1063/1.4905234 View Table of Contents: http://scitation.aip.org/content/aip/journal/jmp/56/1?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Local well-posedness for nonlinear Klein-Gordon equation with weak and strong d...
Long-term evolution of strongly nonlinear internal solitary waves in a rotating channel
Directory of Open Access Journals (Sweden)
J. C. Sánchez-Garrido
2009-09-01
Full Text Available The evolution of internal solitary waves (ISWs propagating in a rotating channel is studied numerically in the framework of a fully-nonlinear, nonhydrostatic numerical model. The aim of modelling efforts was the investigation of strongly-nonlinear effects, which are beyond the applicability of weakly nonlinear theories. Results reveal that small-amplitude waves and sufficiently strong ISWs evolve differently under the action of rotation. At the first stage of evolution an initially two-dimensional ISW transforms according to the scenario described by the rotation modified Kadomtsev-Petviashvili equation, namely, it starts to evolve into a Kelvin wave (with exponential decay of the wave amplitude across the channel with front curved backwards. This transition is accompanied by a permanent radiation of secondary Poincaré waves attached to the leading wave. However, in a strongly-nonlinear limit not all the energy is transmitted to secondary radiated waves. Part of it returns to the leading wave as a result of nonlinear interactions with secondary Kelvin waves generated in the course of time. This leads to the formation of a slowly attenuating quasi-stationary system of leading Kelvin waves, capable of propagating for several hundreds hours as a localized wave packet.
A method for regulating strong nonlinear vibration energy of the flexible arm
Directory of Open Access Journals (Sweden)
Yushu Bian
2015-07-01
Full Text Available For an oscillating system, large amplitude indicates strong vibration energy. In this article, modal interaction is used as a useful means to regulate strong nonlinear vibration energy of the flexible arm undergoing rigid motion. A method is put forward to migrate and dissipate vibration energy based on modal interaction. By means of multiple-scale perturbation analysis, it is proven that internal resonance can be successfully established between modes of the flexible arm and the vibration absorber. Through examples and analyses, it is verified that this control method is effective in regulating strong vibration energy and can be used to suppress strong nonlinear vibration of the flexible arm undergoing rigid motion.
A novel strong tracking finite-difference extended Kalman filter for nonlinear eye tracking
Institute of Scientific and Technical Information of China (English)
ZHANG ZuTao; ZHANG JiaShu
2009-01-01
Non-Intrusive methods for eye tracking are Important for many applications of vision-based human computer interaction. However, due to the high nonlinearity of eye motion, how to ensure the robust-ness of external interference and accuracy of eye tracking poses the primary obstacle to the integration of eye movements into today's interfaces. In this paper, we present a strong tracking finite-difference extended Kalman filter algorithm, aiming to overcome the difficulty In modeling nonlinear eye tracking. In filtering calculation, strong tracking factor is introduced to modify a priori covariance matrix and im-prove the accuracy of the filter. The filter uses finite-difference method to calculate partial derivatives of nonlinear functions for eye tracking. The latest experimental results show the validity of our method for eye tracking under realistic conditions.
A method for regulating strong nonlinear vibration energy of the flexible arm
Yushu Bian; Ming Wang; Zhihui Gao; Baofeng Yuan; Ming Fan
2015-01-01
For an oscillating system, large amplitude indicates strong vibration energy. In this article, modal interaction is used as a useful means to regulate strong nonlinear vibration energy of the flexible arm undergoing rigid motion. A method is put forward to migrate and dissipate vibration energy based on modal interaction. By means of multiple-scale perturbation analysis, it is proven that internal resonance can be successfully established between modes of the flexible arm and the vibration ab...
Three-step Iterations with Errors for Nonlinear Strongly Accretive Operator Equations
Institute of Scientific and Technical Information of China (English)
Ke Su
2005-01-01
In this paper, we suggest and analyse a three-step iterative scheme with errors for solving nonlinear strongly accretive operator equation Tx = f without the Lipshitz condition. The results presented in this paper improve and extend current results in the more general setting.
DEFF Research Database (Denmark)
Thomsen, Jon Juel
2006-01-01
Effects of strong high-frequency excitation at multiple frequencies (multi-HFE) are analyzed for a class of generally nonlinear systems. The effects are illustrated for a simple pendulum system with a vibrating support, and for a parametrically excited flexible beam. For the latter, theoretical...
A New Approach to Duffing Equation with Strong and High Order Nonlinearity
Institute of Scientific and Technical Information of China (English)
JianguoLIN
1999-01-01
A new parameter iteration technique is proposed to solve the Duffing equation with strong and high order nonlinearity,Contrary to the linearized perturbation technique parametrized perturbation technique and variational iteration technique proposed by J.H.He,the frequency converged asymptotically to the exact result,not a constant.
Luo, X. W.; Xu, P.; Sun, C. W.; Jin, H.; Hou, R. J.; Leng, H. Y.; Zhu, S. N.
2017-06-01
Concurrent spontaneous parametric down-conversion (SPDC) processes have proved to be an appealing approach for engineering the path-entangled photonic state with designable and tunable spatial modes. In this work, we propose a general scheme to construct high-dimensional path entanglement and demonstrate the basic properties of concurrent SPDC processes from domain-engineered quadratic nonlinear photonic crystals, including the spatial modes and the photon flux, as well as the anisotropy of spatial correlation under noncollinear quasi-phase-matching geometry. The overall understanding about the performance of concurrent SPDC processes will give valuable references to the construction of compact path entanglement and the development of new types of photonic quantum technologies.
Application of new novel energy balance method to strongly nonlinear oscillator systems
Directory of Open Access Journals (Sweden)
Md. Abdur Razzak
2015-01-01
Full Text Available In this paper, a new novel energy balance method based on the harmonic balance method is proposed to obtain higher-order approximations of strongly nonlinear problems arising in engineering. Especially, second-order approximation is considered in this paper. Results found in this paper are compared with the exact result and other existing results. The results show that the proposed method gives better result for both small and large amplitudes of oscillation than other existing results. The method is illustrated by examples. It has been shown that the proposed method is very effective, convenient and quite accurate to nonlinear engineering problems.
Modeling of Nonlinear Propagation in Multi-layer Biological Tissues for Strong Focused Ultrasound
Institute of Scientific and Technical Information of China (English)
FAN Ting-Bo; LIU Zhen-Bo; ZHANG Zhe; ZHANG DONG; GONG Xiu-Fen
2009-01-01
A theoretical model of the nonlinear propagation in multi-layered tissues for strong focused ultrasound is proposed. In this model, the spheroidal beam equation (SBE) is utilized to describe the nonlinear sound propagation in each layer tissue, and generalized oblique incidence theory is used to deal with the sound transmission between two layer tissues. Computer simulation is performed on a fat-muscle-liver tissue model under the irradiation of a 1 MHz focused transducer with a large aperture angle of 35°. The results demonstrate that the tissue layer would change the amplitude of sound pressure at the focal region and cause the increase of side petals.
Anisotropy of Nonlinear-Optical Property of RCOB (R ＝ Gd, Y) Crystal
Institute of Scientific and Technical Information of China (English)
WANG Zheng-Ping; WEI Jing-Qian; CHEN Huan-Chu; SHAO Zong-Shu; LIU Jun-Hai; SONG Ren-Bo; JIANG Huai-Dong; ZHANG Shu-Jun; FU Kun; WANG Chang-Qing; WANG Ji-Yang; LIU Yao-Gang
2001-01-01
The nonlinear-optical coefficients of RCOB (R ＝ Gd, Y) crystals are measured. The spatial distribution of deff (effective nonlinear-optical coefficient) is subsequently determined. Our experiments show that the maximum deff occurs at the second quadrant. The second-harmonic generation efficiency reaches 48% for a 6 mm long, (113.2°,47.4°)-cut GdCOB, and 41.5% for a 5mm long, (113°, 36.5°)-cut YCOB, respectively. The intracavity frequency doubling of GdCOB is reported for the first time.
Notes on the nonlinear beam dynamics with strong damping in the CLIC Damping Ring
Levichev, Eugene; Shatilov, Dmitry
2010-01-01
The beam is injected into the CLIC damping ring with the relatively large emittance and energy spread and then is damped to the extremely low phase volume. During the damping process the betatron frequency of each particle changes due to the space charge tune shift and nonlinear dependence of the betatron tune on the amplitude. This nonlinearity is produced by the strong chromatic sextupoles, wiggler nonlinear field components and, again, by the space charge force. During the damping, the particle cross resonances, which can trap some fraction of the beam, cause the loss of intensity, the beam blow up and degrade the beam quality. In this paper we study the evolution of the beam distribution in time during the damping for the original lattice of the CLIC DR (May 2005). Geneva, Switzerland June 2010 CLIC – Note – 850
Clack, C
2009-01-01
The nonlinear theory of driven magnetohydrodynamics (MHD) waves in strongly anisotropic and dispersive plasmas, developed for slow resonance by Clack and Ballai [Phys. Plasmas, 15, 2310 (2008)] and Alfv\\'en resonance by Clack \\emph{et al.} [A&A,494, 317 (2009)], is used to study the weakly nonlinear interaction of fast magnetoacoustic (FMA) waves in a one-dimensional planar plasma. The magnetic configuration consists of an inhomogeneous magnetic slab sandwiched between two regions of semi-infinite homogeneous magnetic plasmas. Laterally driven FMA waves penetrate the inhomogeneous slab interacting with the localized slow or Alfv\\'{e}n dissipative layer and are partly reflected, dissipated and transmitted by this region. The nonlinearity parameter defined by Clack and Ballai (2008) is assumed to be small and a regular perturbation method is used to obtain analytical solutions in the slow dissipative layer. The effect of dispersion in the slow dissipative layer is to further decrease the coefficient of ener...
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
A new procedure is proposed to construct strongly nonlinear systems of multiple degrees of freedom subjected to parametric and/or external Gaussian white noises, whose exact stationary solutions are independent of energy. Firstly, the equivalent Fokker-Planck-Kolmogorov (FPK) equations are derived by using exterior differentiation. The main difference between the equivalent FPK equation and the original FPK equation lies in the additional arbitrary antisymmetric diffusion matrix. Then the exact stationary solutions and the structures of the original systems can be obtained by using the coefficients of antisymmetric diffusion matrix. The obtained exact stationary solutions, which are generally independent of energy, are for the most general class of strongly nonlinear stochastic systems multiple degrees of freedom (MDOF) so far, and some classes of the known ones dependent on energy belong to the special cases of them.
Institute of Scientific and Technical Information of China (English)
HUANG ZhiLong; JIN XiaoLing
2009-01-01
A new procedure is proposed to construct strongly nonlinear systems of multiple degrees of freedom subjected to parametric and/or external Gaussian white noises,whose exact stationary solutions are independent of energy.Firstly,the equivalent Fokker-Planck-Kolmogorov(FPK)equations are derived by using exterior differentiation.The main difference between the equivalent FPK equation and the original FPK equation lies in the additional arbitrary antisymmetric diffusion matrix.Then the exact stationary solutions and the structures of the original systems can be obtained by using the coefficients of antisymmetric diffusion matrix.The obtained exact stationary solutions,which are generally independent of energy,are for the most general class of strongly nonlinear stochastic systems multiple degrees of freedom(MDOF)so far,and some classes of the known ones dependent on energy belong to the special cases of them.
Institute of Scientific and Technical Information of China (English)
Changshui Feng; Weiqiu Zhu
2008-01-01
A bounded optimal control strategy for strongly non-linear systems under non-white wide-band random excitation with actuator saturation is proposed. First, the stochastic averaging method is introduced for controlled strongly non-linear systems under wide-band random excitation using generalized harmonic functions. Then, the dynamical programming equation for the saturated control problem is formulated from the partially averaged Ito equation based on the dynamical programming principle. The optimal control consisting of the unbounded optimal control and the bounded bang-bang control is determined by solving the dynamical programming equation. Finally, the response of the optimally controlled system is predicted by solving the reduced Fokker-Planck-Kolmogorov (FPK) equation associated with the completed averaged Ito equation. An example is given to illustrate the proposed control strategy. Numerical results show that the proposed control strategy has high control effectiveness and efficiency and the chattering is reduced significantly comparing with the bang-bang control strategy.
Strong quantum squeezing near the pull-in instability of a nonlinear beam
Passian, Ali; Siopsis, George
2016-08-01
Microscopic silicon-based suspended mechanical oscillators, constituting an extremely sensitive force probe, transducer, and actuator, are being increasingly employed in many developing microscopies, spectroscopies, and emerging optomechanical and chem-bio sensors. We predict a significant squeezing in the quantum state of motion of an oscillator constrained as a beam and subject to an electrically induced nonlinearity. By taking into account the quantum noise, the underlying nonlinear dynamics is investigated in both the transient and stationary regimes of the driving force leading to the finding that strongly squeezed states are accessible in the vicinity of the pull-in instability of the oscillator. We discuss a possible application of this strong quantum squeezing as an optomechanical method for detecting broad-spectrum single or low-count photons, and further suggest other novel sensing actions.
Propagation of a Laguerre-Gaussian correlated Schell-model beam in strongly nonlocal nonlinear media
Qiu, Yunli; Chen, Zhaoxi; He, Yingji
2017-04-01
Analytical expressions for the cross-spectral density function and the second-order moments of the Wigner distribution function of a Laguerre-Gaussian correlated Schell-model (LGCSM) beam propagating in strongly nonlocal nonlinear media are derived. The propagation properties, such as beam irradiance, beam width, the spectral degree of coherence and the propagation factor of a LGCSM beam inside the media are investigated in detail. The effect of the beam parameters and the input power on the evolution properties of a LGCSM is illustrated numerically. It is found that the beam width varies periodically or keeps invariant for a certain proper input power. And both the beam irradiance and the spectral degree of coherence of the LGCSM beam change periodically with the propagation distance for the arbitrary input power which however has no influence on the propagation factor. The coherent length and the mode order mainly affect the evolution speed of the LGCSM beam in strongly nonlocal nonlinear media.
Nonlinear quantum optics in the (ultra)strong light-matter coupling
Sánchez-Burillo, Eduardo; García-Ripoll, Juan José; Martín-Moreno, Luis; Zueco, David
2014-01-01
The propagation of $N$ photons in one dimensional waveguides coupled to $M$ qubits is discussed, both in the strong and ultrastrong qubit-waveguide coupling. Special emphasis is placed on the characterisation of the nonlinear response and its linear limit for the scattered photons as a function of $N$, $M$, qubit inter distance and light-matter coupling. The quantum evolution is numerically solved via the Matrix Product States technique. Both the time evolution for the field and qubits is com...
Global Stability and Dynamics of Strongly Nonlinear Systems Using Koopman Operator Theory
2017-03-01
calculus, applied mathematics, Director’s Research Initiative 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU 18...ARL-TR-7959 MAR 2017 US Army Research Laboratory Global Stability and Dynamics of Strongly Nonlinear Systems Using Koopman...report when it is no longer needed. Do not return it to the originator. ARL-TR-7959 ● MAR 2017 US Army Research Laboratory Global
Reyes-Esqueda, Jorge Alejandro; Rodríguez-Iglesias, Vladimir; Silva-Pereyra, Héctor-Gabriel; Torres-Torres, Carlos; Santiago-Ramírez, Ana-Laura; Cheang-Wong, Juan Carlos; Crespo-Sosa, Alejandro; Rodríguez-Fernández, Luis; López-Suárez, Alejandra; Oliver, Alicia
2009-07-20
High-energy metallic ions were implanted in silica matrices, obtaining spherical-like metallic nanoparticles (NPs) after a proper thermal treatment. These NPs were then deformed by irradiation with Si ions, obtaining an anisotropic metallic nanocomposite. An average large birefringence of 0.06 was measured for these materials in the 300-800 nm region. Besides, their third order nonlinear optical response was measured using self-diffraction and P-scan techniques at 532 nm with 26 ps pulses. By adjusting the incident light's polarization and the angular position of the nanocomposite, the measurements could be directly related to, at least, two of the three linear independent components of its third order susceptibility tensor, finding a large, but anisotropic, response of around 10(-7) esu with respect to other isotropic metallic systems. For the nonlinear optical absorption, we were able to shift from saturable to reverse saturable absorption depending on probing the Au NP's major or minor axes, respectively. This fact could be related to local field calculations and NP's electronic properties. For the nonlinear optical refraction, we passed from self-focusing to self-defocusing, when changing from Ag to Au.
Linear and nonlinear heavy ion-acoustic waves in a strongly coupled plasma
Energy Technology Data Exchange (ETDEWEB)
Ema, S. A., E-mail: ema.plasma@gmail.com; Mamun, A. A. [Department of Physics, Jahangirnagar University, Savar, Dhaka-1342 (Bangladesh); Hossen, M. R. [Deparment of Natural Sciences, Daffodil International University, Sukrabad, Dhaka-1207 (Bangladesh)
2015-09-15
A theoretical study on the propagation of linear and nonlinear heavy ion-acoustic (HIA) waves in an unmagnetized, collisionless, strongly coupled plasma system has been carried out. The plasma system is assumed to contain adiabatic positively charged inertial heavy ion fluids, nonextensive distributed electrons, and Maxwellian light ions. The normal mode analysis is used to study the linear behaviour. On the other hand, the well-known reductive perturbation technique is used to derive the nonlinear dynamical equations, namely, Burgers equation and Korteweg-de Vries (K-dV) equation. They are also numerically analyzed in order to investigate the basic features of shock and solitary waves. The adiabatic effects on the HIA shock and solitary waves propagating in such a strongly coupled plasma are taken into account. It has been observed that the roles of the adiabatic positively charged heavy ions, nonextensivity of electrons, and other plasma parameters arised in this investigation have significantly modified the basic features (viz., polarity, amplitude, width, etc.) of the HIA solitary/shock waves. The findings of our results obtained from this theoretical investigation may be useful in understanding the linear as well as nonlinear phenomena associated with the HIA waves both in space and laboratory plasmas.
Analytical approximate technique for strongly nonlinear oscillators problem arising in engineering
Directory of Open Access Journals (Sweden)
Y. Khan
2012-12-01
Full Text Available In this paper, a novel method called generalized of the variational iteration method is presented to obtain an approximate analytical solution for strong nonlinear oscillators problem associated in engineering phenomena. This approach resulted in the frequency of the motion as a function of the amplitude of oscillation. It is determined that the method works very well for the whole range of parameters and an excellent agreement is demonstrated and discussed between the approximate frequencies and the exact one. The most significant features of this method are its simplicity and excellent accuracy for the whole range of oscillation amplitude values. Also, the results reveal that this technique is very effective and convenient for solving conservative oscillatory systems with complex nonlinearities. Results obtained by the proposed method are compared with Energy Balance Method (EBM and exact solution showed that, contrary to EBM, simply one or two iterations are enough for obtaining highly accurate results.
A new nonlinear conjugate gradient coefficient under strong Wolfe-Powell line search
Mohamed, Nur Syarafina; Mamat, Mustafa; Rivaie, Mohd
2017-08-01
A nonlinear conjugate gradient method (CG) plays an important role in solving a large-scale unconstrained optimization problem. This method is widely used due to its simplicity. The method is known to possess sufficient descend condition and global convergence properties. In this paper, a new nonlinear of CG coefficient βk is presented by employing the Strong Wolfe-Powell inexact line search. The new βk performance is tested based on number of iterations and central processing unit (CPU) time by using MATLAB software with Intel Core i7-3470 CPU processor. Numerical experimental results show that the new βk converge rapidly compared to other classical CG method.
Escape time from potential wells of strongly nonlinear oscillators with slowly varying parameters
Directory of Open Access Journals (Sweden)
Cai Jianping
2005-01-01
Full Text Available The effect of negative damping to an oscillatory system is to force the amplitude to increase gradually and the motion will be out of the potential well of the oscillatory system eventually. In order to deduce the escape time from the potential well of quadratic or cubic nonlinear oscillator, the multiple scales method is firstly used to obtain the asymptotic solutions of strongly nonlinear oscillators with slowly varying parameters, and secondly the character of modulus of Jacobian elliptic function is applied to derive the equations governing the escape time. The approximate potential method, instead of Taylor series expansion, is used to approximate the potential of an oscillation system such that the asymptotic solution can be expressed in terms of Jacobian elliptic function. Numerical examples verify the efficiency of the present method.
Nonlinear coda wave analysis of hysteretic elastic behavior in strongly scattering media
Ouarabi, M. Ait; Boubenider, F.; Gliozzi, A. S.; Scalerandi, M.
2016-10-01
Strongly scattering elastic media, such as consolidated granular materials, respond to ultrasonic pulse excitations with a long response signal with peculiar properties. The portion of the signal at late times, termed coda, is due to multiple scattering. It contains information about the elastic properties of the material, and it has been proven to be very sensitive to small variations in the modulus. Here we propose a technique based on a nonlinear analysis of the coda of a signal, which might be applied to quantify the nonlinear elastic response in consolidated granular media exhibiting a hysteretic elastic behavior. The method proposed allows for an intrinsic definition of the reference signal which is normally needed for applying coda-based methods.
Attractors for strongly damped wave equations with nonlinear hyperbolic dynamic boundary conditions
Jameson Graber, P.; Shomberg, Joseph L.
2016-04-01
We establish the well-posedness of a strongly damped semilinear wave equation equipped with nonlinear hyperbolic dynamic boundary conditions. Results are carried out with the presence of a parameter distinguishing whether the underlying operator is analytic, α >0 , or only of Gevrey class, α =0 . We establish the existence of a global attractor for each α \\in ≤ft[0,1\\right], and we show that the family of global attractors is upper-semicontinuous as α \\to 0. Furthermore, for each α \\in ≤ft[0,1\\right] , we show the existence of a weak exponential attractor. A weak exponential attractor is a finite dimensional compact set in the weak topology of the phase space. This result ensures the corresponding global attractor also possesses finite fractal dimension in the weak topology; moreover, the dimension is independent of the perturbation parameter α. In both settings, attractors are found under minimal assumptions on the nonlinear terms.
Nonlinear interaction of charged particles with strong laser pulses in a gaseous media
Directory of Open Access Journals (Sweden)
H. K. Avetissian
2007-07-01
Full Text Available The charged particles nonlinear dynamics in the field of a strong electromagnetic wave pulse of finite duration and certain form of the envelope, in the refractive medium with a constant and variable refraction indexes, is investigated by means of numerical integration of the classical relativistic equations of motion. The particle energy dependence on the pulse intensity manifests the nonlinear threshold phenomenon of a particle reflection and capture by actual laser pulses in dielectric-gaseous media that takes place for a plane electromagnetic wave in the induced Cherenkov process. Laser acceleration of the particles in the result of the reflection from the pulse envelope and in the capture regime with the variable refraction index along the pulse propagation direction is investigated.
Young-Gonzales, Amanda R; Samanta, Subarna; Richert, Ranko
2015-09-14
For glycerol and three monohydroxy alcohols, we have measured the non-linear dielectric effects resulting from the application and removal of a high dc bias electric field. The field effects are detected by virtue of a small amplitude harmonic field, from which time resolved changes in the dielectric loss are derived. The changes in permittivity are dominated by modifications of the time constants (rather than amplitudes) which display two contributions: a heating-like decrease of relaxation times that originates from the time dependent field when the bias is switched on and off and a slowing down of the dynamics resulting from the field induced reduction of configurational entropy. As observed for the electro-optical Kerr effect, the rise of the entropy change is slower than its decay, a feature that we rationalize on the basis of the quadratic dependence of the entropy change on polarization. For glycerol, the observed steady state level of the field induced shift of the glass transition temperature (+84 mK) matches the expectation based on the entropy change and its impact on dynamics via the Adam-Gibbs relation (+88 mK). For the alcohols, these non-linear effects rise and decay on the time scales of the prominent dielectric Debye process, underscoring the relation of these features to polarization anisotropy, opposed to mechanical or enthalpy relaxation which are orders of magnitude faster in these systems. A model is discussed which captures the observed magnitudes as well as time dependences in a near quantitative fashion. It is demonstrated that the high bias field modifies the response of polarization to the ac field, including a temporary change in the low field susceptibility.
Integrated nanoplasmonic waveguides for magnetic, nonlinear, and strong-field devices
Sederberg, Shawn; Firby, Curtis J.; Greig, Shawn R.; Elezzabi, Abdulhakem Y.
2017-01-01
As modern complementary-metal-oxide-semiconductor (CMOS) circuitry rapidly approaches fundamental speed and bandwidth limitations, optical platforms have become promising candidates to circumvent these limits and facilitate massive increases in computational power. To compete with high density CMOS circuitry, optical technology within the plasmonic regime is desirable, because of the sub-diffraction limited confinement of electromagnetic energy, large optical bandwidth, and ultrafast processing capabilities. As such, nanoplasmonic waveguides act as nanoscale conduits for optical signals, thereby forming the backbone of such a platform. In recent years, significant research interest has developed to uncover the fundamental physics governing phenomena occurring within nanoplasmonic waveguides, and to implement unique optical devices. In doing so, a wide variety of material properties have been exploited. CMOS-compatible materials facilitate passive plasmonic routing devices for directing the confined radiation. Magnetic materials facilitate time-reversal symmetry breaking, aiding in the development of nonreciprocal isolators or modulators. Additionally, strong confinement and enhancement of electric fields within such waveguides require the use of materials with high nonlinear coefficients to achieve increased nonlinear optical phenomenon in a nanoscale footprint. Furthermore, this enhancement and confinement of the fields facilitate the study of strong-field effects within the solid-state environment of the waveguide. Here, we review current state-of-the-art physics and applications of nanoplasmonic waveguides pertaining to passive, magnetoplasmonic, nonlinear, and strong-field devices. Such components are essential elements in integrated optical circuitry, and each fulfill specific roles in truly developing a chip-scale plasmonic computing architecture.
Blow-Up Analysis for a Quasilinear Degenerate Parabolic Equation with Strongly Nonlinear Source
Directory of Open Access Journals (Sweden)
Pan Zheng
2012-01-01
Full Text Available We investigate the blow-up properties of the positive solution of the Cauchy problem for a quasilinear degenerate parabolic equation with strongly nonlinear source ut=div(|∇um|p−2∇ul+uq, (x,t∈RN×(0,T, where N≥1, p>2 , and m, l, q>1, and give a secondary critical exponent on the decay asymptotic behavior of an initial value at infinity for the existence and nonexistence of global solutions of the Cauchy problem. Moreover, under some suitable conditions we prove single-point blow-up for a large class of radial decreasing solutions.
Using strong nonlinearity and high-frequency vibrations to control effective mechanical stiffness
DEFF Research Database (Denmark)
Thomsen, Jon Juel
2008-01-01
High-frequency excitation (HFE) can be used to change the effective stiffness of an elastic structure, and related quanti-ties such as resonance frequencies, wave speed, buckling loads, and equilibrium states. There are basically two ways to do this: By using parametrical HFE (with or without non...... the method of direct separation of motions with results of a modified multiple scales ap-proach, valid also for strong nonlinearity, the stiffening ef-fect is predicted for a generic 1-dof system, and results are tested against numerical simulation and ((it is planned)) laboratory experiments....
Strong micro-macro entanglement from a weak cross-Kerr nonlinearity
Wang, Tian; Kaviani, Hamidreza; Ghobadi, Roohollah; Simon, Christoph
2014-01-01
We study the entanglement generated by a weak cross-Kerr nonlinearity between two initial coherent states, one of which has an amplitude close to the single-photon level, while the other one is macroscopic. We show that strong micro-macro entanglement is possible for weak phase shifts by choosing the amplitude of the macroscopic beam sufficiently large. We analyze the effects of loss and discuss possible experimental demonstrations of the micro-macro entanglement based on homodyne tomography and on a new entanglement witness.
Using strong nonlinearity and high-frequency vibrations to control effective mechanical stiffness
DEFF Research Database (Denmark)
Thomsen, Jon Juel
2008-01-01
High-frequency excitation (HFE) can be used to change the effective stiffness of an elastic structure, and related quanti-ties such as resonance frequencies, wave speed, buckling loads, and equilibrium states. There are basically two ways to do this: By using parametrical HFE (with or without non...... the method of direct separation of motions with results of a modified multiple scales ap-proach, valid also for strong nonlinearity, the stiffening ef-fect is predicted for a generic 1-dof system, and results are tested against numerical simulation and ((it is planned)) laboratory experiments....
Strongly nonlinear models for internal waves: an application for the dam-break problem
Chen, Shengqian
2016-01-01
Strongly nonlinear models of internal wave propagation for incompressible stratified Euler fluids are investigated numerically and analytically to determine the evolution of a class of initial conditions of interest in laboratory experiments. This class of step-like initial data severely tests the robustness of the models beyond their strict long-wave asymptotic validity, and model fidelity is assessed by direct numerical simulations (DNS) of the parent Euler system. It is found that the primary dynamics of near-solitary wave formation is remarkably well predicted by the models for both wave and fluid properties, at a fraction of the computational costs of the DNS code.
Strong perpendicular magnetic anisotropy in Co2FeAl0.5Si0.5 film sandwiched by MgO layers
Institute of Scientific and Technical Information of China (English)
Wang Sheng; Li Xiao-Qi; Bai Li-Juan; Xu Xiao-Guang; Miao Jun; Jiang Yong
2013-01-01
Co2FeAl0.5Si0.5 (CFAS)-based multilayers sandwiched by MgO layers have been deposited and annealed at different temperatures.Perpendicular magnetic anisotropy (PMA) with the magnetic anisotropy energy density Ku ≈2.5× 106 erg/cm3 (1 erg =10-7 J) and the coercivity Hc =363 Oe (1Oe =79.9775 A.m-1) has been achieved in the Si/SiO2/MgO (1.5 nm)/CFAS (2.5 nm)/MgO (0.8 nm)/Pt (5 nm) film annealed at 300 ℃.The strong PMA is mainly due to the top MgO layer.The structure can be used as top magnetic electrodes in half-metallic perpendicular magnetic tunnel junctions.
Gajek, Wojciech; Verdon, James; Malinowski, Michał; Trojanowski, Jacek
2017-04-01
Azimuthal anisotropy plays a key-role in hydraulic fracturing experiments, since it provides information on stress orientation and pre-existing fracture system presence. The Lower Paleozoic shale plays in northern Poland are characterized by a strong (15-18%) Vertical Transverse Isotropy (VTI) fabric which dominates weak azimuthal anisotropy being of order of 1-2%. A shear wave travelling in the subsurface after entering an anisotropic medium splits into two orthogonally polarized waves travelling with different velocities. Splitting parameters which can be assessed using a microseismic array are polarization of the fast shear wave and time delay between two modes. Polarization of the fast wave characterizes the anisotropic system on the wave path while the time delay is proportional to the magnitude of anisotropy. We employ Shear Wave Splitting (SWS) technique using a borehole microseismic dataset collected during a hydraulic stimulation treatment located in northern Poland, to image fracture strike masked by a strong VTI signature. During the inversion part, the VTI background parameters were kept constant using information from 3D seismic (VTI model used for pre-stack depth migration). Obtained fracture azimuths averaged over fracturing stages are consistent with the available XRMI imager logs from the nearby vertical well, however they are different from the large-scale maximum stress direction (by 40-45 degrees). Inverted Hudson's crack density (ca. 2%) are compatible with the low shear-wave anisotropy observed in the cross-dipole sonic logs (1-2%). This work has been funded by the Polish National Centre for Research and Development within the Blue Gas project (No BG2/SHALEMECH/14). Data were provided by the PGNiG SA. Collaboration with University of Bristol was supported within TIDES COST Action ES1401.
Response Regimes in Equivalent Mechanical Model of Strongly Nonlinear Liquid Sloshing
Farid, M
2016-01-01
We consider equivalent mechanical model of liquid sloshing in partially-filled cylindrical vessel; the model treats both the regime of linear sloshing, and strongly nonlinear sloshing regime. The latter is related to hydraulic impacts applied to the vessel walls. These hydraulic impacts are commonly simulated with the help of high-power potential and dissipation functions. For the sake of analytic exploration, we substitute this traditional approach by treatment of an idealized vibro-impact system with velocity-dependent restitution coefficient. The obtained reduced model is similar to recently explored system of linear primary oscillator with attached vibro-impact energy sink. The ratio of modal mass of the first sloshing mode to the total mass of the liquid and the tank serves as a natural small parameter for multiple-scale analysis. In the case of external ground forcing, steady-state responses and chaotic strongly modulated responses are revealed. All analytical predictions of the reduced vibro-impact mod...
Strong anisotropy effect in an iron-based superconductor CaFe0.882Co0.118AsF
Ma, Yonghui; Ji, Qiucheng; Hu, Kangkang; Gao, Bo; Li, Wei; Mu, Gang; Xie, Xiaoming
2017-07-01
The anisotropy of iron-based superconductors is much smaller than that of the cuprates and that predicted by theoretical calculations. A credible understanding for this experimental fact is still lacking up to now. Here we experimentally study the magnetic-field-angle dependence of electronic resistivity in the superconducting phase of an iron-based superconductor CaFe{}0.882Co{}0.118AsF, and find the strongest anisotropy effect of the upper critical field among the iron-based superconductors based on the framework of Ginzburg-Landau theory. The evidence of the energy band structure and charge density distribution from electronic structure calculations demonstrates that the observed strong anisotropic effect mainly comes from the strong ionic bonding in between the ions of Ca2+ and F-, which weakens the interlayer coupling between the layers of FeAs and CaF. This finding provides a significant insight into the nature of the experimentally-observed strong anisotropic effect of electronic resistivity, and also paves the way for designing exotic two-dimensional artificial unconventional superconductors in the future.
Strong Glacial Cooling In The Middle Tropical Troposphere Due To Non-linear Effects
Lorenz, S. J.; Lohmann, G.
Numerical experiments with an atmospheric general circulation model for glacial and interglacial climates have been performed. Our model experiments reveal that slightly cooler tropical sea surface temperatures (SST) relative to the ones previously recon- structed by the CLIMAP project (1981) are sufficient to exhibit a strong glacial cool- ing reconstructed by tropical snow lines. The increased cooling in our experiments can be attributed to two non-linear effects: Firstly, there is an increased environmental lapse rate in the free atmosphere. Slightly cooler glacial SSTs provide for less abso- lute moisture content and the Clausius-Clapeyron equation of moisture is accountable for an increased lapse rate. In our LGM simulation we find an additional two degrees cooling in the tropical middle troposphere. Secondly, the surface air temperature near tropical glaciers is further cooled by a longer duration of snow cover. Our model result provides a consistent view of the last glacial maximum climate with much colder tem- peratures than today in the tropical mountains in concordance with moderate lowering of tropical SSTs. We propose that these non-linearities in the climate system are also important when detecting global warming from tropical snow lines.
Institute of Scientific and Technical Information of China (English)
Chang-shui FENG; Wei-qiu ZHU
2009-01-01
We studied the response of harmonically and stochastically excited strongly nonlinear oscillators with delayed feedback bang-bang control using the stochastic averaging method. First, the time-delayed feedback bang-bang control force is expressed approximately in terms of the system state variables without time delay. Then the averaged Ito stochastic differential equations for the system are derived using the stochastic averaging method. Finally, the response of the system is obtained by solving the Fokker-Plank-Kolmogorov (FPK) equation associated with the averaged Ito equations. A Duffing oscillator with time-delayed feedback bang-bang control under combined harmonic and white noise excitations is taken as an example to illus-trate the proposed method. The analytical results are confirmed by digital simulation. We found that the time delay in feedback bang-bang control will deteriorate the control effectiveness and cause bifurcation of stochastic jump of Duffing oscillator.
Semiclassical description of nonlinear electron-positron photoproduction in strong laser fields
Meuren, Sebastian; Di Piazza, Antonino
2015-01-01
The nonlinear Breit-Wheeler process is studied in the presence of strong and short laser pulses. We show that for a relativistically intense plane-wave laser field many aspects of the momentum distribution for the produced electron-positron pair like its extend, region of highest probability and carrier-envelope phase effects can be explained from the classical evolution of the created particles in the background field. To this end we verify that the local constant-crossed field approximation is also appropriate for the calculation of the spectrum if applied on the probability-amplitude level. To compare the exact expressions with the semiclassical approach, we introduce a very fast numerical scheme, which makes it feasible to completely resolve the interference structure of the spectrum over the available multidimensional phase space.
Directory of Open Access Journals (Sweden)
Md. Alal Hosen
2015-01-01
Full Text Available In the present paper, a complicated strongly nonlinear oscillator with cubic and harmonic restoring force, has been analysed and solved completely by harmonic balance method (HBM. Investigating analytically such kinds of oscillator is very difficult task and cumbersome. In this study, the offered technique gives desired results and to avoid numerical complexity. An excellent agreement was found between approximate and numerical solutions, which prove that HBM is very efficient and produces high accuracy results. It is remarkably important that, second-order approximate results are almost same with exact solutions. The advantage of this method is its simple procedure and applicable for many other oscillatory problems arising in science and engineering.
Nonlinear Brillouin amplification of finite-duration seeds in the strong coupling regime
Lehmann, G.; Spatschek, K. H.
2013-07-01
Parametric plasma processes received renewed interest in the context of generating ultra-intense and ultra-short laser pulses up to the exawatt-zetawatt regime. Both Raman as well as Brillouin amplifications of seed pulses were proposed. Here, we investigate Brillouin processes in the one-dimensional (1D) backscattering geometry with the help of numerical simulations. For optimal seed amplification, Brillouin scattering is considered in the so called strong coupling (sc) regime. Special emphasis lies on the dependence of the amplification process on the finite duration of the initial seed pulses. First, the standard plane-wave instability predictions are generalized to pulse models, and the changes of initial seed pulse forms due to parametric instabilities are investigated. Three-wave-interaction results are compared to predictions by a new (kinetic) Vlasov code. The calculations are then extended to the nonlinear region with pump depletion. Generation of different seed layers is interpreted by self-similar solutions of the three-wave interaction model. Similar to Raman amplification, shadowing of the rear layers by the leading layers of the seed occurs. The shadowing is more pronounced for initially broad seed pulses. The effect is quantified for Brillouin amplification. Kinetic Vlasov simulations agree with the three-wave interaction predictions and thereby affirm the universal validity of self-similar layer formation during Brillouin seed amplification in the strong coupling regime.
Directory of Open Access Journals (Sweden)
V. I. Vlasenko
Full Text Available For many lakes the nonlinear transfer of energy from basin-scale internal waves to short-period motions, such as solitary internal waves (SIW and wave trains, their successive interaction with lake boundaries, as well as over-turning and breaking are important mechanisms for an enhanced mixing of the turbulent benthic boundary layer. In the present paper, the evolution of plane SIWs in a variable depth channel, typical of a lake of variable depth, is considered, with the basis being the Reynolds equations. The vertical fluid stratification, wave amplitudes and bottom parameters are taken close to those observed in Lake Constance, a typical mountain lake. The problem is solved numerically. Three different scenarios of a wave evolution over variable bottom topography are examined. It is found that the basic parameter controlling the mechanism of wave evolution is the ratio of the wave amplitude to the distance from the metalimnion to the bottom d. At sites with a gentle sloping bottom, where d is small, propagating (weak or strong internal waves adjust to the local ambient conditions and preserve their form. No secondary waves or wave trains arise during wave propagation from the deep part to the shallow water. If the amplitude of the propagating waves is comparable with the distance between the metalimnion and the top of the underwater obstacle ( d ~ 1, nonlinear dispersion plays a key role. A wave approaching the bottom feature splits into a sequence of secondary waves (solitary internal waves and an attached oscillating wave tail. The energy of the SIWs above the underwater obstacle is transmitted in parts from the first baroclinic mode, to the higher modes. Most crucially, when the internal wave propagates from the deep part of a basin to the shallow boundary, a breaking event can arise. The cumulative effects of the nonlinearity lead to a steepening and
High-frequency effects in 1D spring-mass systems with strongly non-linear inclusions
DEFF Research Database (Denmark)
Lazarov, Boyan Stefanov; Snaeland, S.O.; Thomsen, Jon Juel
2010-01-01
-like systems with embedded non-linear parts, where the masses interact with a limited set of neighbour masses. The presented analytical and numerical results show that the effective properties for LF wave propagation can be altered by establishing HF standing waves in the non-linear regions of the chain......This work generalises the possibilities to change the effective material or structural properties for low frequency (LF) wave propagation, by using high-frequency (HF) external excitation combined with strong non-linear and non-local material behaviour. The effects are demonstrated on 1D chain....... The changes affect the effective stiffness and damping of the system....
Elastic anisotropy of crystals
Directory of Open Access Journals (Sweden)
Christopher M. Kube
2016-09-01
Full Text Available An anisotropy index seeks to quantify how directionally dependent the properties of a system are. In this article, the focus is on quantifying the elastic anisotropy of crystalline materials. Previous elastic anisotropy indices are reviewed and their shortcomings discussed. A new scalar log-Euclidean anisotropy measure AL is proposed, which overcomes these deficiencies. It is based on a distance measure in a log-Euclidean space applied to fourth-rank elastic tensors. AL is an absolute measure of anisotropy where the limiting case of perfect isotropy yields zero. It is a universal measure of anisotropy applicable to all crystalline materials. Specific examples of strong anisotropy are highlighted. A supplementary material provides an anisotropy table giving the values of AL for 2,176 crystallite compounds.
Nonlinear response of the quantum Hall system to a strong electromagnetic radiation
Avetissian, H. K.; Mkrtchian, G. F.
2016-12-01
We study nonlinear response of a quantum Hall system in semiconductor-hetero-structures via third harmonic generation process and nonlinear Faraday effect. We demonstrate that Faraday rotation angle and third harmonic radiation intensity have a characteristic Hall plateaus feature. These nonlinear effects remain robust against the significant broadening of Landau levels. We predict realization of an experiment through the observation of the third harmonic signal and Faraday rotation angle, which are within the experimental feasibility.
Anderson, Johan; Johansson, Jonas
2016-12-01
An analytical derivation of the probability density function (PDF) tail describing the strongly correlated interface growth governed by the nonlinear Kardar-Parisi-Zhang equation is provided. The PDF tail exactly coincides with a Tracy-Widom distribution i.e. a PDF tail proportional to \\exp ≤ft(-cw23/2\\right) , where w 2 is the the width of the interface. The PDF tail is computed by the instanton method in the strongly non-linear regime within the Martin-Siggia-Rose framework using a careful treatment of the non-linear interactions. In addition, the effect of spatial dimensions on the PDF tail scaling is discussed. This gives a novel approach to understand the rightmost PDF tail of the interface width distribution and the analysis suggests that there is no upper critical dimension.
Nonlinear propagation of strong-field THz pulses in doped semiconductors
DEFF Research Database (Denmark)
Turchinovich, Dmitry; Hvam, Jørn Märcher; Hoffmann, Matthias C.
2012-01-01
We report on nonlinear propagation of single-cycle THz pulses with peak electric fields reaching 300 kV/cm in n-type semiconductors at room temperature. Dramatic THz saturable absorption effects are observed in GaAs, GaP, and Ge, which are caused by the nonlinear electron transport in THz fields....
Energy Technology Data Exchange (ETDEWEB)
Haug, Daniel; Hinkov, Vladimir; Lin, Chengtian; Keimer, Bernhard [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Fauque, Benoit; Bourges, Philippe; Sidis, Yvan [Laboratoire Leon Brillouin, CEA-CNRS Saclay (France); Ivanov, Alexandre [Institut Laue-Langevin, Grenoble (France)
2008-07-01
The spin excitation spectrum of the optimally doped and moderately underdoped high-temperature superconductor YBa{sub 2}Cu{sub 3}O{sub 6+x} is dominated by the so-called resonance peak for excitation energies between 30 and 40 meV (depending on the oxygen content x) that sets in abruptly below T{sub c}. Here we report measurements on arrays of untwinned single crystals in the strongly underdoped regime in which the situation is very different: Spectral weight is shifted towards low energies and evolves smoothly through T{sub c}. The spectrum exhibits a peak below {proportional_to}10 meV which shows a spontaneous onset of a strong anisotropy in the a-b-plane defined by the CuO{sub 2} layers. This phenomenon matches the symmetry properties of a nematic liquid crystal, a new symmetry-broken electronic phase that coexists with high-temperature superconductivity in strongly underdoped cuprates.
Energy Technology Data Exchange (ETDEWEB)
Granitzer, P. [Institute of Physics, Karl Franzens University Graz, Universtaetsplatz 5, 8010 Graz (Austria)]. E-mail: petra.granitzer@uni-graz.at; Rumpf, K. [Institute of Physics, Karl Franzens University Graz, Universtaetsplatz 5, 8010 Graz (Austria); Poelt, P. [Institute for Electron Microscopy, University of Technology Graz, Steyrergasse 17, 8010 Graz (Austria); Reichmann, A. [Institute for Electron Microscopy, University of Technology Graz, Steyrergasse 17, 8010 Graz (Austria); Krenn, H. [Institute of Physics, Karl Franzens University Graz, Universtaetsplatz 5, 8010 Graz (Austria)
2007-03-15
The electrochemically fabricated porous silicon (PS) exhibits pores that are oriented perpendicular to the surface and arranged in a quadratic-like manner. These quasi-regular, self-assembled channels are filled with Ni in a further electrolytic process to produce an array of quasi-regular ferromagnetic nanostructures. This ferromagnetic nanocomposite can be tailored concerning structure and magnetic behavior by varying the electrochemical parameters due to the PS fabrication as well as to the metal filling procedure. Structural characterization (SEM, EDXS) proves the Ni-content within the porous layer. Magnetization measurements show an anisotropic ferromagnetic behavior. Zero-field-cooled (ZFC)/field-cooled (FC) measurements indicate that the size distribution of the incorporated Ni-nanostructures is rather broad, but these magnetization curves may also indicate strong coupling.
Fan, Ting-Bo; Liu, Zhen-Bo; Zhang, Zhe; Zhang, Dong; Gong, Xiu-Fen
2009-08-01
A theoretical model of the nonlinear propagation in multi-layered tissues for strong focused ultrasound is proposed. In this model, the spheroidal beam equation (SBE) is utilized to describe the nonlinear sound propagation in each layer tissue, and generalized oblique incidence theory is used to deal with the sound transmission between two layer tissues. Computer simulation is performed on a fat-muscle-liver tissue model under the irradiation of a 1 MHz focused transducer with a large aperture angle of 35°. The results demonstrate that the tissue layer would change the amplitude of sound pressure at the focal region and cause the increase of side petals.
Garai, S.; Janaki, M. S.; Chakrabarti, N.
2016-09-01
The nonlinear propagation of low frequency waves, in a collisionless, strongly coupled dusty plasma (SCDP) with a density dependent viscosity, has been studied with a proper Galilean invariant generalized hydrodynamic (GH) model. The well known reductive perturbation technique (RPT) has been employed in obtaining the solutions of the longitudinal and transverse perturbations. It has been found that the nonlinear propagation of the acoustic perturbations govern with the modified Korteweg-de Vries (KdV) equation and are decoupled from the sheared fluctuations. In the regions, where transversal gradients of the flow exists, coupling between the longitudinal and transverse perturbations occurs due to convective nonlinearity which is true for the homogeneous case also. The results, obtained here, can have relative significance to astrophysical context as well as in laboratory plasmas.
Akbarzade, M.; Langari, J.
2011-02-01
In this paper a new approach combining the features of the homotopy concept with variational approach is proposed to find accurate analytical solutions for nonlinear oscillators with and without a fractional power restoring force. Since the first-order approximation leads to very accurate results, comparisons with other results are presented to show the effectiveness of this method. The validity of the method is independent of whether or not there exist small or large parameters in the considered nonlinear equations; the obtained results prove the validity and efficiency of the method, which can be easily extended to other strongly nonlinear problems. At the end we compare our procedure with the optimal homotopy perturbation method.
Gottlieb, Sigal
2015-04-10
High order spatial discretizations with monotonicity properties are often desirable for the solution of hyperbolic PDEs. These methods can advantageously be coupled with high order strong stability preserving time discretizations. The search for high order strong stability time-stepping methods with large allowable strong stability coefficient has been an active area of research over the last two decades. This research has shown that explicit SSP Runge-Kutta methods exist only up to fourth order. However, if we restrict ourselves to solving only linear autonomous problems, the order conditions simplify and this order barrier is lifted: explicit SSP Runge-Kutta methods of any linear order exist. These methods reduce to second order when applied to nonlinear problems. In the current work we aim to find explicit SSP Runge-Kutta methods with large allowable time-step, that feature high linear order and simultaneously have the optimal fourth order nonlinear order. These methods have strong stability coefficients that approach those of the linear methods as the number of stages and the linear order is increased. This work shows that when a high linear order method is desired, it may still be worthwhile to use methods with higher nonlinear order.
Energy Technology Data Exchange (ETDEWEB)
Belendez, A. [Departamento de Fisica, Ingenieria de Sistemas y Teoria de la Senal, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain)], E-mail: a.belendez@ua.es; Gimeno, E.; Alvarez, M.L.; Mendez, D.I.; Hernandez, A. [Departamento de Fisica, Ingenieria de Sistemas y Teoria de la Senal, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain)
2008-09-22
An analytical approximate technique for conservative nonlinear oscillators is proposed. This method is a modification of the rational harmonic balance method in which analytical approximate solutions have rational form. This approach gives us the frequency of the motion as a function of the amplitude of oscillation. We find that this method works very well for the whole range of parameters, and excellent agreement of the approximate frequencies with the exact one has been demonstrated and discussed. The most significant features of this method are its simplicity and its excellent accuracy for the whole range of oscillation amplitude values and the results reveal that this technique is very effective and convenient for solving conservative truly nonlinear oscillatory systems with complex nonlinearities.
Directory of Open Access Journals (Sweden)
Banan Maayah
2014-01-01
Full Text Available A new algorithm called multistep reproducing kernel Hilbert space method is represented to solve nonlinear oscillator’s models. The proposed scheme is a modification of the reproducing kernel Hilbert space method, which will increase the intervals of convergence for the series solution. The numerical results demonstrate the validity and the applicability of the new technique. A very good agreement was found between the results obtained using the presented algorithm and the Runge-Kutta method, which shows that the multistep reproducing kernel Hilbert space method is very efficient and convenient for solving nonlinear oscillator’s models.
Non trivial effect of strong high-frequency excitation on a nonlinear controlled system
DEFF Research Database (Denmark)
Fidlin, A.; Thomsen, Jon Juel
2004-01-01
due to control is usually high compared to uncontrolled systems. A standard optimal controller for a standard nonlinear system (a movable cart used to balance a pendulum vertically) is shown to exhibit pronounced bias error in presence of HF-excitation. The bias increases with increased excitation...
Numerical Analysis of Strongly Nonlinear Oscillation Systems using He's Max-Min Method
DEFF Research Database (Denmark)
Babazadeh, H; Domairry, G; Barari, Amin;
2011-01-01
Nonlinear functions are crucial points and terms in engineering problems. Actual and physical problems can be solved by solving and processing such functions. Thus, most scientists and engineers focus on solving these equations. This paper presents a novel method called the max-min method...
Directory of Open Access Journals (Sweden)
Yan-Lei Zhang
2016-01-01
Full Text Available Nonlinear vibration of a fluid-conveying pipe subjected to a transverse external harmonic excitation is investigated in the case with two-to-one internal resonance. The excitation amplitude is in the same magnitude of the transverse displacement. The fluid in the pipes flows in the speed larger than the critical speed so that the straight configuration becomes an unstable equilibrium and two curved configurations bifurcate as stable equilibriums. The motion measured from each of curved equilibrium configurations is governed by a nonlinear integro-partial-differential equation with variable coefficients. The Galerkin method is employed to discretize the governing equation into a gyroscopic system consisting of a set of coupled nonlinear ordinary differential equations. The method of multiple scales is applied to analyze approximately the gyroscopic system. A set of first-order ordinary differential equations governing the modulations of the amplitude and the phase are derived via the method. In the supercritical regime, the subharmonic, superharmonic, and combination resonances are examined in the presence of the 2 : 1 internal resonance. The steady-state responses and their stabilities are determined. The various jump phenomena in the amplitude-frequency response curves are demonstrated. The effects of the viscosity, the excitation amplitude, the nonlinearity, and the flow speed are observed. The analytical results are supported by the numerical integration.
2010-03-01
indeed studied the dynamics of our systems at impulses approaching speeds 750 m /s and preliminary analyses using state of the art hydrocodes17...These systems, now referred to as deco - rated TCs DTCs, represent a significant improvement and turn out to be strongly nonlinear in their...presented. Hard sphere approximations for both systems follow in Sec. III. Section IV outlines the numerical approach and results for the deco - rated chain
Beneš, Michal
2010-01-01
The present paper deals with mathematical models of heat and moisture transport in layered building envelopes. The study of such processes generates a system of two doubly nonlinear evolution partial differential equations with appropriate initial and boundary conditions. The existence of the strong solution in two dimensions on a (short) time interval is proven. The proof rests on regularity results for elliptic transmission problem for composite-like materials.
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
Quasi-likelihood nonlinear models (QLNM) include generalized linear models as a special case.Under some regularity conditions,the rate of the strong consistency of the maximum quasi-likelihood estimation (MQLE) is obtained in QLNM.In an important case,this rate is O(n-1/2(loglogn)1/2),which is just the rate of LIL of partial sums for I.I.d variables,and thus cannot be improved anymore.
Strong anisotropy within a Heisenberg model in the Jeff=1/2 insulating state of Sr2Ir0.8Ru0.2O4
Calder, S.; Kim, J. W.; Taylor, A. E.; Upton, M. H.; Casa, D.; Cao, Guixin; Mandrus, D.; Lumsden, M. D.; Christianson, A. D.
2016-12-01
The dispersive magnetic excitations in Sr2IrO4 have previously been well described within an isospin-1/2 Heisenberg model on a square lattice that revealed parallels with La2CuO4 . Here we investigate the inelastic spectra of Sr2Ir0.8Ru0.2O4 with resonant inelastic x-ray scattering (RIXS) at the Ir L3 edge. The results are well described using linear spin-wave theory within a similar Heisenberg model applicable to Sr2IrO4 ; however, the disorder induced by the substitution of 20 %Ir4 + ions for Ru4 + removes longer range exchange interactions. A large spin gap (40 meV) is measured indicating strong anisotropy from spin-orbit coupling that is manifest due to the altered magnetic structure in Sr2Ir0.8Ru0.2O4 with c -axis aligned moments compared to the basal plane moments in the parent. Collectively the results indicate the robustness of a Heisenberg model description even when the magnetic structure is altered and the Jeff=1 /2 moments are diluted.
The optimal antenna for nonlinear spectroscopy of weakly and strongly scattering nanoobjects
Schumacher, Thorsten; Brandstetter, Matthias; Wolf, Daniela; Kratzer, Kai; Hentschel, Mario; Giessen, Harald; Lippitz, Markus
2016-04-01
Optical nanoantennas, i.e., arrangements of plasmonic nanostructures, promise to enhance the light-matter interaction on the nanoscale. In particular, nonlinear optical spectroscopy of single nanoobjects would profit from such an antenna, as nonlinear optical effects are already weak for bulk material, and become almost undetectable for single nanoobjects. We investigate the design of optical nanoantennas for transient absorption spectroscopy in two different cases: the mechanical breathing mode of a metal nanodisk and the quantum-confined carrier dynamics in a single CdSe nanowire. In the latter case, an antenna with a resonance at the desired wavelength optimally increases the light intensity at the nanoobject. In the first case, the perturbation of the antenna by the investigated nanosystem cannot be neglected and off-resonant antennas become most efficient.
Energy Technology Data Exchange (ETDEWEB)
Ella, Lior, E-mail: lior.ella@weizmann.ac.il; Yuvaraj, D.; Suchoi, Oren; Shtempluk, Oleg; Buks, Eyal [Faculty of Electrical Engineering, Technion, Haifa 32000 (Israel)
2015-01-07
We present a study of the controllable nonlinear dynamics of a micromechanical beam coupled to a dc-SQUID (superconducting quantum interference device). The coupling between these systems places the modes of the beam in a highly nonlinear potential, whose shape can be altered by varying the bias current and applied flux of the SQUID. We detect the position of the beam by placing it in an optical cavity, which sets free the SQUID to be used solely for actuation. This enables us to probe the previously unexplored full parameter space of this device. We measure the frequency response of the beam and find that it displays a Duffing oscillator behavior which is periodic in the applied magnetic flux. To account for this, we develop a model based on the standard theory for SQUID dynamics. In addition, with the aim of understanding if the device can reach nonlinearity at the single phonon level, we use this model to show that the responsivity of the current circulating in the SQUID to the position of the beam can become divergent, with its magnitude limited only by noise. This suggests a direction for the generation of macroscopically distinguishable superposition states of the beam.
Experimental study of strong nonlinear-optics effects in liquid crystals
Darbin, S. D.; Arakelyan, S. M.; Cheung, M. M.; Shen, Y. R.
1984-07-01
Nonlinear optical effects that arise in nematic liquid crystals as a result of a change in the index of refraction induced by a laser field are considered. Since the resultant nonlinearity is extremely high, the approximation of perturbation theory cannot be used in calculations. However, the change in refractive index results mainly in phase advance as waves propagate through a thin film of liquid crystal, while the change of intensity is significant. Moreover, if there is no change in polarization of the pumping field, calculations are relatively simple. An investigation is made of the propagation of a cross sectionally bounded laser beam through a homeotropically oriented liquid crystal, giving rise to spatial phase modulation of emission. When the intensity of the laser beam exceeds a certain value, a system of aberation rings is observed in the output radiation. Effects of dynamic self-diffraction accompanying degenerate four-wave mixing when a change in refractive index is induced in a homeotropic liquid crystal film, and optical bistability in a nonlinear Fabry-Perot optical cavity, as well as generation of a self-oscillatory state in such a resonator are discussed.
Nonlinear interaction of charged particles with strong laser pulses in a magnetic undulator
Directory of Open Access Journals (Sweden)
H. K. Avetissian
2010-08-01
Full Text Available Laser acceleration due to the nonlinear-threshold phenomena of charged particle “reflection” and capture by slowed wave in a magnetic undulator is considered. The obtained numerical results prove the particle reflection and capture phenomena in the field of actual laser pulses with temporal and space profiles which lead to the particles acceleration. In contrast to the reflection regime where particle acceleration takes place already at the constant undulator step, in the capture regime it is necessary to increase adiabatically the undulator step along the laser pulse propagation direction by the certain self-consistent variation law corresponding to acceleration rate.
Accelerating oscillatory fronts in a nonlinear sonic vacuum with strong nonlocal effects.
Gendelman, O V; Zolotarevskiy, V; Savin, A V; Bergman, L A; Vakakis, A F
2016-03-01
We describe and explore accelerating oscillatory fronts in sonic vacua with nonlocal interactions. As an example, a chain of particles oscillating in the plane and coupled by linear springs, with fixed ends, is considered. When one end of this system is harmonically excited in the transverse direction, one observes accelerated propagation of the excitation front, accompanied by an almost monochromatic oscillatory tail. Position of the front obeys the scaling law l(t) ∼ t(4/3). The frequency of the oscillatory tail remains constant, and the wavelength scales as λ ∼ t(1/3). These scaling laws result from the nonlocal effects; we derive them analytically (including the scaling coefficients) from a continuum approximation. Moreover, a certain threshold excitation amplitude is required in order to initiate the front propagation. The initiation threshold is evaluated on the basis of a simplified discrete model, further reduced to a completely integrable nonlinear system. Given their simplicity, nonlinear sonic vacua of the type considered herein should be common in periodic lattices.
Non-linear quantum dynamics in strong and short electromagnetic fields
Titov, Alexander I; Hosaka, Atsushi; Takabe, Hideaki
2016-01-01
In our contribution we give a brief overview of two widely discussed quantum processes: electron-positron pairs production off a probe photon propagating through a polarized short-pulsed electromagnetic (e.m.) (e.g.\\ laser) wave field or generalized Breit-Wheeler process and a single a photon emission off an electron interacting with the laser pules, so-called non-linear Compton scattering. We show that at small and moderate laser field intensities the shape and duration of the pulse are very important for the probability of considered processes. However, at high intensities the multi-photon interactions of the fermions with laser field are decisive and completely determined all aspects of subthreshold electron-positron pairs and photon production
DEFF Research Database (Denmark)
Nysteen, Anders; McCutcheon, Dara; Mørk, Jesper
2015-01-01
We analytically treat the scattering of two counterpropagating photons on a two-level emitter embedded in an optical waveguide. We find that the nonlinearity of the emitter can give rise to significant pulse-dependent directional correlations in the scattered photonic state, which could...... be quantified via a reduction in coincidence clicks in a Hong–Ou–Mandel measurement setup, analogous to a linear beam splitter. Changes to the spectra and phase of the scattered photons, however, would lead to reduced interference with other photons when implemented in a larger optical circuit. We introduce...... suitable fidelity measures which account for these changes and find that high values can still be achieved even when accounting for all properties of the scattered photonic state....
Lange, C; Hohenleutner, M; Baierl, S; Schubert, O; Edwards, E; Bougeard, D; Woltersdorf, G; Huber, R
2016-01-01
Terahertz near fields of gold metamaterials resonant at a frequency of $0.88\\,\\rm THz$ allow us to enter an extreme limit of non-perturbative ultrafast THz electronics: Fields reaching a ponderomotive energy in the keV range are exploited to drive nondestructive, quasi-static interband tunneling and impact ionization in undoped bulk GaAs, injecting electron-hole plasmas with densities in excess of $10^{19}\\,\\rm cm^{-3}$. This process causes bright luminescence at energies up to $0.5\\,\\rm eV$ above the band gap and induces a complete switch-off of the metamaterial resonance accompanied by self-amplitude modulation of transmitted few-cycle THz transients. Our results pave the way towards highly nonlinear THz optics and optoelectronic nanocircuitry with sub-picosecond switching times.
Tanjia, Fatema; Fedele, Renato; Shukla, P K; Jovanovic, Dusan
2011-01-01
A numerical analysis of the self-interaction induced by a relativistic electron/positron beam in the presence of an intense external longitudinal magnetic field in plasmas is carried out. Within the context of the Plasma Wake Field theory in the overdense regime, the transverse beam-plasma dynamics is described by a quantumlike Zakharov system of equations in the long beam limit provided by the Thermal Wave Model. In the limiting case of beam spot size much larger than the plasma wavelength, the Zakharov system is reduced to a 2D Gross-Pitaevskii-type equation, where the trap potential well is due to the external magnetic field. Vortices, "beam halos" and nonlinear coherent states (2D solitons) are predicted.
Johansson, Magnus; Derevyanko, Stanislav A
2013-01-01
We investigate the mobility of nonlinear localized modes in a one-dimensional waveguide array in an active Kerr medium with intrinsic, saturable gain and damping, described by a generalized discrete Ginzburg-Landau type model. It is shown that exponentially localized, traveling discrete dissipative breather-solitons may exist as stable attractors supported only by intrinsic properties of the medium, i.e., in absence of any external field or symmetry-breaking perturbations. Through an interplay by the gain and damping effects, the moving soliton may overcome the Peierls-Nabarro barrier, present in the corresponding conservative system, by self-induced time-periodic oscillations of its power (norm) and energy (Hamiltonian), yielding exponential decays to zero with different rates in the forward and backward directions. In certain parameter windows, bistability appears between fast modes with small oscillations, and slower, large-oscillation modes. The velocities and the oscillation periods are typically related...
Remick, Kevin; Dane Quinn, D.; Michael McFarland, D.; Bergman, Lawrence; Vakakis, Alexander
2016-05-01
The authors investigate a vibration-based energy harvesting system utilizing essential (nonlinearizable) nonlinearities and electromagnetic coupling elements. The system consists of a grounded, weakly damped linear oscillator (primary system) subjected to a single impulsive load. This primary system is coupled to a lightweight, damped oscillating attachment (denoted as nonlinear energy sink, NES) via a neodymium magnet and an inductance coil, and a piano wire, which generates an essential geometric cubic stiffness nonlinearity. Under impulsive input, the transient damped dynamics of this system exhibit transient resonance captures (TRCs) causing intentional large-amplitude and high-frequency instabilities in the response of the NES. These TRCs result in strong energy transfer from the directly excited primary system to the light-weight attachment. The energy is harvested by the electromagnetic elements in the coupling and, in the present case, dissipated in a resistive element in the electrical circuit. The primary goal of this work is to numerically, analytically, and experimentally demonstrate the efficacy of employing this type of intentional high-frequency dynamic instability to achieve enhanced vibration energy harvesting under impulsive excitation.
Non-Linear Compton Scattering in a Strong Rotating Electric Field
Raicher, Erez; Zigler, Arie
2016-01-01
The non-linear Compton scattering rate in a rotating electric field is explicitly calculated for the first time. For this purpose, a novel solution to the Klein-Gordon equation in the presence of a rotating electric field is applied. An analytical expression for the emission rate is obtained, as well as a simplified approximation adequate for emplementation in kinetic codes. The spectrum is numerically calculated for nowadays optical and X-ray laser parameters. The results are compared to the standard Volkov-Ritus rate for a particle in a plane wave, which is commonly assumed to be valid for a rotating electric field under certain conditions. Subsequent deviations between the two models, both in the radiated power and the spectral shape, are demonstrated. First, the typical number of photons participating in the scattering process is much smaller compared to the Volkov-Ritus rate, resulting in up to an order of magnitude lower emitted power. Furthermore, our model predicts a discrete harmonics spectrum for el...
Directory of Open Access Journals (Sweden)
Jaroslav Jaroš
2015-01-01
Full Text Available We consider \\(n\\-dimensional cyclic systems of second order differential equations \\[(p_i(t|x_{i}'|^{\\alpha_i -1}x_{i}'' = q_{i}(t|x_{i+1}|^{\\beta_i-1}x_{i+1},\\] \\[\\quad i = 1,\\ldots,n, \\quad (x_{n+1} = x_1 \\tag{\\(\\ast\\}\\] under the assumption that the positive constants \\(\\alpha_i\\ and \\(\\beta_i\\ satisfy \\(\\alpha_1{\\ldots}\\alpha_n \\gt \\beta_1{\\ldots}\\beta_n\\ and \\(p_i(t\\ and \\(q_i(t\\ are regularly varying functions, and analyze positive strongly increasing solutions of system (\\(\\ast\\ in the framework of regular variation. We show that the situation for the existence of regularly varying solutions of positive indices for (\\(\\ast\\ can be characterized completely, and moreover that the asymptotic behavior of such solutions is governed by the unique formula describing their order of growth precisely. We give examples demonstrating that the main results for (\\(\\ast\\ can be applied to some classes of partial differential equations with radial symmetry to acquire accurate information about the existence and the asymptotic behavior of their radial positive strongly increasing solutions.
DEFF Research Database (Denmark)
Sorokin, Vladislav; Thomsen, Jon Juel
2015-01-01
Parametrically excited systems appear in many fields of science and technology, intrinsically or imposed purposefully; e.g. spatially periodic structures represent an important class of such systems [4]. When the parametric excitation can be considered weak, classical asymptotic methods like...... the method of averaging [2] or multiple scales [6] can be applied. However, with many practically important applications this simplification is inadequate, e.g. with spatially periodic structures it restricts the possibility to affect their effective dynamic properties by a structural parameter modulation...... of considerable magnitude. Approximate methods based on Floquet theory [4] for analyzing problems involving parametric excitation, e.g. the classical Hill’s method of infinite determinants [3,4], can be employed also in cases of strong excitation; however, with Floquet theory being applicable only for linear...
A nonlinear equation for ionic diffusion in a strong binary electrolyte
Ghosal, Sandip; 10.1098/rspa.2010.0028
2012-01-01
The problem of the one dimensional electro-diffusion of ions in a strong binary electrolyte is considered. In such a system the solute dissociates completely into two species of ions with unlike charges. The mathematical description consists of a diffusion equation for each species augmented by transport due to a self consistent electrostatic field determined by the Poisson equation. This mathematical framework also describes other important problems in physics such as electron and hole diffusion across semi-conductor junctions and the diffusion of ions in plasmas. If concentrations do not vary appreciably over distances of the order of the Debye length, the Poisson equation can be replaced by the condition of local charge neutrality first introduced by Planck. It can then be shown that both species diffuse at the same rate with a common diffusivity that is intermediate between that of the slow and fast species (ambipolar diffusion). Here we derive a more general theory by exploiting the ratio of Debye length...
Strong and nonlinear effects of fragmentation on ecosystem service provision at multiple scales
Mitchell, Matthew G. E.; Bennett, Elena M.; Gonzalez, Andrew
2015-09-01
Human actions, such as converting natural land cover to agricultural or urban land, result in the loss and fragmentation of natural habitat, with important consequences for the provision of ecosystem services. Such habitat loss is especially important for services that are supplied by fragments of natural land cover and that depend on flows of organisms, matter, or people across the landscape to produce benefits, such as pollination, pest regulation, recreation and cultural services. However, our quantitative knowledge about precisely how different patterns of landscape fragmentation might affect the provision of these types of services is limited. We used a simple, spatially explicit model to evaluate the potential impact of natural land cover loss and fragmentation on the provision of hypothetical ecosystem services. Based on current literature, we assumed that fragments of natural land cover provide ecosystem services to the area surrounding them in a distance-dependent manner such that ecosystem service flow depended on proximity to fragments. We modeled seven different patterns of natural land cover loss across landscapes that varied in the overall level of landscape fragmentation. Our model predicts that natural land cover loss will have strong and unimodal effects on ecosystem service provision, with clear thresholds indicating rapid loss of service provision beyond critical levels of natural land cover loss. It also predicts the presence of a tradeoff between maximizing ecosystem service provision and conserving natural land cover, and a mismatch between ecosystem service provision at landscape versus finer spatial scales. Importantly, the pattern of landscape fragmentation mitigated or intensified these tradeoffs and mismatches. Our model suggests that managing patterns of natural land cover loss and fragmentation could help influence the provision of multiple ecosystem services and manage tradeoffs and synergies between services across different human
Anderson, Miles; Coen, Stéphane; Erkintalo, Miro; Murdoch, Stuart G
2016-01-01
Localized dissipative structures (LDS) have been predicted to display a rich array of instabilities, yet systematic experimental studies have remained scarce. We have used a synchronously-driven optical fiber ring resonator to experimentally study LDS instabilities in the strong-driving regime of the AC-driven nonlinear Schr\\"odinger equation (also known as the Lugiato-Lefever model). Through continuous variation of a single control parameter, we have observed a string of theoretically predicted instability modes, including irregular oscillations and chaotic collapses. Beyond a critical point, we observe behaviour reminiscent of a phase transition: LDSs trigger localized domains of spatiotemporal chaos that invade the surrounding homogeneous state. Our findings directly confirm a number of theoretical predictions, and they highlight that complex LDS instabilities can play a role in experimental systems.
Monthus, Cécile
2004-02-01
We study the dynamics in the one-dimensional disordered trap model with a broad distribution of trapping times p(tau) approximately 1/tau(1+mu), when an external force is applied from the very beginning at t=0, or only after a waiting time t(w), in the linear as well as in the nonlinear response regime. Using a real-space renormalization procedure that becomes exact in the limit of strong disorder mu-->0, we obtain explicit results for many observables, such as the diffusion front, the mean position, the thermal width, the localization parameters and the two-particle correlation function. In particular, the scaling functions for these observables give access to the complete interpolation between the unbiased case and the directed case. Finally, we discuss in detail the various regimes that exist for the average position in terms of the two times and the external field.
Ema, S. A.; Hossen, M. R.; Mamun, A. A.
2016-04-01
The nonlinear propagation of ion-acoustic (IA) waves in a strongly coupled plasma system containing Maxwellian electrons and nonthermal ions has been theoretically and numerically investigated. The well-known reductive perturbation technique is used to derive both the Burgers and Korteweg-de Vries (KdV) equations. Their shock and solitary wave solutions have also been numerically analyzed in understanding localized electrostatic disturbances. It has been observed that the basic features (viz. polarity, amplitude, width, etc.) of IA waves are significantly modified by the effect of polarization force and other plasma parameters (e.g., the electron-to-ion number density ratio and ion-to-electron temperature ratio). This is a unique finding among all theoretical investigations made before, whose probable implications are discussed in this investigation. The implications of the results obtained from this investigation may be useful in understanding the wave propagation in both space and laboratory plasmas.
Anisotropy of a cubic ferromagnet at criticality
Kudlis, A.; Sokolov, A. I.
2016-10-01
Critical fluctuations change the effective anisotropy of cubic ferromagnet near the Curie point. If the crystal undergoes phase transition into orthorhombic phase and the initial anisotropy is not too strong, reduced anisotropy of nonlinear susceptibility acquires at Tc the universal value δ4*=2/v* 3 (u*+v*) where u* and v* are coordinates of the cubic fixed point on the flow diagram of renormalization group equations. In the paper, the critical value of the reduced anisotropy is estimated within the pseudo-ɛ expansion approach. The six-loop pseudo-ɛ expansions for u*, v*, and δ4* are derived for the arbitrary spin dimensionality n . For cubic crystals (n =3 ) higher-order coefficients of the pseudo-ɛ expansions obtained turn out to be so small that use of simple Padé approximants yields reliable numerical results. Padé resummation of the pseudo-ɛ series for u*, v*, and δ4* leads to the estimate δ4*=0.079 ±0.006 , indicating that detection of the anisotropic critical behavior of cubic ferromagnets in physical and computer experiments is certainly possible.
Gu, Zhiping
This paper extends Riccati transfer matrix method to the transient and stability analysis of large scale rotor-bearing systems with strong nonlinear elements, and proposes a mode summation-transfer matrix method, in which the field transfer matrix of a distributed mass uniform shaft segment is obtained with the aid of the idea of mode summation and Newmark beta formulation, and the Riccati transfer matrix method is adopted to stablize the boundary value problem of the nonlinear systems. In this investigation, the real nonlinearity of the strong nonlinear elements is considered, not linearized, and the advantages of the Riccati transfer matrix are retained. So, this method is especially applicable to analyze the transient response and stability of large-scale rotor-bear systems with strong nonlinear elements. One example, a single-spool rotating system with strong nonlinear elements, is given. The obtained results show that this method is superior to that of Gu and Chen (1990) in accuracy, stability, and economy.
Okuzumi, Satoshi
2014-01-01
The MHD of protoplanetary disks crucially depends on the ionization state of the disks. Recent simulations suggest that MHD turbulence in the disks can generate a strong electric field in the local rest frame. Such a strong field can heat up plasmas and thereby change the ionization balance. To study this effect, we construct a charge reaction model that includes plasma heating by electric fields and impact ionization by heated electrons, as well as plasma accretion by dust grains. The resulting Ohm's law is nonlinear in the electric field strength. We find that the gas-phase electron abundance decreases with increasing the electric field strength when plasma accretion onto grains dominates over gas-phase recombination, because electron heating accelerates electron--grain collisions. This leads to an increase in the magnetic resistivity, and possibly to a self-regulation of the MHD turbulence. In some cases, even the electric current decreases with increasing the field strength in a certain field range. The N...
Hmiel, A.; Winey, J. M.; Gupta, Y. M.; Desjarlais, M. P.
2016-05-01
Accurate theoretical calculations of the nonlinear elastic response of strong solids (e.g., diamond) constitute a fundamental and important scientific need for understanding the response of such materials and for exploring the potential synthesis and design of novel solids. However, without corresponding experimental data, it is difficult to select between predictions from different theoretical methods. Recently the complete set of third-order elastic constants (TOECs) for diamond was determined experimentally, and the validity of various theoretical approaches to calculate the same may now be assessed. We report on the use of density functional theory (DFT) methods to calculate the six third-order elastic constants of diamond. Two different approaches based on homogeneous deformations were used: (1) an energy-strain fitting approach using a prescribed set of deformations, and (2) a longitudinal stress-strain fitting approach using uniaxial compressive strains along the [100], [110], and [111] directions, together with calculated pressure derivatives of the second-order elastic constants. The latter approach provides a direct comparison to the experimental results. The TOECs calculated using the energy-strain approach differ significantly from the measured TOECs. In contrast, calculations using the longitudinal stress-uniaxial strain approach show good agreement with the measured TOECs and match the experimental values significantly better than the TOECs reported in previous theoretical studies. Our results on diamond have demonstrated that, with proper analysis procedures, first-principles calculations can indeed be used to accurately calculate the TOECs of strong solids.
Silantyev, Denis A.; Lushnikov, Pavel M.; Rose, Harvey A.
2017-04-01
We consider two kinds of pumped Langmuir waves (LWs) in the kinetic regime, k λ D ≳ 0.2 , where k is the LW wavenumber and λD is the Debye length, driven to finite amplitude by a coherent external potential whose amplitude is either weak or strong. These dynamically prepared nonlinear LWs develop a transverse (filamentation) instability whose nonlinear evolution destroys the LW's transverse coherence. Instability growth rates in the weakly pumped regime are the same as those of Bernstein-Greene-Kruskal modes considered in Part I (D. A. Silantyev et al., Phys. Plasmas 24, 042104 (2017)), while strongly pumped LWs have higher filamentation grow rates.
Silantyev, Denis A; Rose, Harvey A
2016-01-01
We consider two kinds of pumped Langmuir waves (LWs) in the kinetic regime, $k\\lambda_D\\gtrsim0.2,$ where $k$ is the LW wavenumber and $\\lambda_D$ is the Debye length. They are driven to finite amplitude by a coherent external potential whose amplitude is either weak or strong. These dynamically prepared nonlinear LWs develop a transverse (filamentation) instability whose nonlinear evolution destroys the LW's transverse coherence. Instability growth rates in the weakly pumped regime are the same as those of BGK modes considered in Part I, while strongly pumped LWs have higher filamentation grow rates.
Energy Technology Data Exchange (ETDEWEB)
Kremer, D.; Rachet, F.; Chrysos, M., E-mail: michel.chrysos@univ-angers.fr [LUNAM Université, Université d’Angers, CNRS UMR 6200, Laboratoire MOLTECH-Anjou, 2 Bd Lavoisier, 49045 Angers (France)
2014-01-21
Long known as a fully polarized band with a near vanishing depolarization ratio [η{sub s} = 0.05, W. Holzer and R. Ouillon, Chem. Phys. Lett. 24, 589 (1974)], the 2ν{sub 5} Raman overtone of SF{sub 6} has so far been considered as of having a prohibitively weak anisotropic spectrum [D. P. Shelton and L. Ulivi, J. Chem. Phys. 89, 149 (1988)]. Here, we report the first anisotropic spectrum of this overtone, at room temperature and for 13 gas densities ranging between 2 and 27 amagat. This spectrum is 10 times broader and 50 times weaker than the isotropic counterpart of the overtone [D. Kremer, F. Rachet, and M. Chrysos, J. Chem. Phys. 138, 174308 (2013)] and its profile much more sensitive to pressure effects than the profile of the isotropic spectrum. From our measurements an accurate value for the anisotropy matrix-element |〈000020|Δα|000000〉| was derived and this value was found to be comparable to that of the mean-polarizability ((000020), α{sup ¯} (000000)). Among other conclusions our study offers compelling evidence that, in Raman spectroscopy, highly polarized bands or tiny depolarization ratios are not necessarily incompatible with large polarizability anisotropy transition matrix-elements. Our findings and the way to analyze them suggest that new strategies should be developed on the basis of the complementarity inherent in independent incoherent Raman experiments that run with two different incident-beam polarizations, and on concerted efforts to ab initio calculate accurate data for first and second polarizability derivatives. Values for these derivatives are still rarities in the literature of SF{sub 6}.
Energy Technology Data Exchange (ETDEWEB)
Toselli, G. [ENEA, Centro Ricerche Ezio Clementel, Bologna, (Italy). Dipt. Innovazione; Mirco, A. M. [Bologna Univ., Bologna (Italy). Dipt. di Matematica
1999-07-01
In this technical report the thesis of doctor's degree in Mathematics of A.M. Mirco is reported; it has been developed at ENEA research centre 'E. Clementel' in Bologna (Italy) in the frame of a collaboration between the section MACO (Applied Physics Division - Innovation Department) of ENEA at Bologna and the Department of Mathematics of the mathematical, physical and natural sciences faculty of Bologna University. Substantially, studies and research work, developed in these last years at MACO section, are here presented; they have led to the development of a constitutive model, based on Hill potential theory, for the treatment, in plastic field, of metal material anisotropy induced by previous workings and to the construction of the corresponding FEM algorithm for the non-linear structural analysis NOSA, oriented in particular to the numerical simulation of metal forming. Subsequently, an algorithm extension (proper object of the thesis), which has given, beyond a more rigorous formalization, also significant improvements. [Italian] In questo rapporto tecnico viene riportata la tesi di laurea in matematica di A. M. Mirco, tesi svolta presso il centro ricerche E. Clementel dell'ENEA di Bologna nell'ambito di un accordo di collaborazione fra la sezione MACO (Divisione Fisica Applicata - Dipartimento di Innovazione) dell'ENEA di Bologna ed il Dipartimento di matematica della facolta' di scienze matematiche, fisiche e naturali dell'universita' degli studi di Bologna. Sostanzialmente, vengono presentati gli studi ed il lavoro di ricerca, svolti in questi ultimi anni presso la sezione MACO, che hanno portato allo sviluppo di un modello costitutivo, basato sulla teoria del potenziale di Hill, per il trattamento in campo plastico, dell'anisotropia indotta da lavorazioni precedenti per un materiale metallico ed alla costruzione del corrispondente algoritmo basato sul metodo degli elementi finiti per il codice di analisi
Augustin, Christoph M.; Neic, Aurel; Liebmann, Manfred; Prassl, Anton J.; Niederer, Steven A.; Haase, Gundolf; Plank, Gernot
2016-01-01
Electromechanical (EM) models of the heart have been used successfully to study fundamental mechanisms underlying a heart beat in health and disease. However, in all modeling studies reported so far numerous simplifications were made in terms of representing biophysical details of cellular function and its heterogeneity, gross anatomy and tissue microstructure, as well as the bidirectional coupling between electrophysiology (EP) and tissue distension. One limiting factor is the employed spatial discretization methods which are not sufficiently flexible to accommodate complex geometries or resolve heterogeneities, but, even more importantly, the limited efficiency of the prevailing solver techniques which is not sufficiently scalable to deal with the incurring increase in degrees of freedom (DOF) when modeling cardiac electromechanics at high spatio-temporal resolution. This study reports on the development of a novel methodology for solving the nonlinear equation of finite elasticity using human whole organ models of cardiac electromechanics, discretized at a high para-cellular resolution. Three patient-specific, anatomically accurate, whole heart EM models were reconstructed from magnetic resonance (MR) scans at resolutions of 220 μm, 440 μm and 880 μm, yielding meshes of approximately 184.6, 24.4 and 3.7 million tetrahedral elements and 95.9, 13.2 and 2.1 million displacement DOF, respectively. The same mesh was used for discretizing the governing equations of both electrophysiology (EP) and nonlinear elasticity. A novel algebraic multigrid (AMG) preconditioner for an iterative Krylov solver was developed to deal with the resulting computational load. The AMG preconditioner was designed under the primary objective of achieving favorable strong scaling characteristics for both setup and solution runtimes, as this is key for exploiting current high performance computing hardware. Benchmark results using the 220 μm, 440 μm and 880 μm meshes demonstrate
Energy Technology Data Exchange (ETDEWEB)
Miles, A
2004-04-27
In core-collapse supernovae, strong blast waves drive interfaces susceptible to Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) instabilities. In addition, perturbation growth can result from material expansion in large-scale velocity gradients behind the shock front. Laser-driven experiments are designed to produce a strongly shocked interface whose evolution is a scaled version of the unstable hydrogen-helium interface in core-collapse supernovae such as SN 1987A. The ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting transition to turbulence on supernovae observables that remain as yet unexplained. In this dissertation, we present a computational study of unstable systems driven by high Mach number shock and blast waves. Using multi-physics radiation hydrodynamics codes and theoretical models, we consider the late nonlinear instability evolution of single mode, few mode, and multimode interfaces. We rely primarily on 2D calculations but present recent 3D results as well. For planar multimode systems, we show that compressibility effects preclude the emergence of a regime of self-similar instability growth independent of the initial conditions (IC's) by allowing for memory of the initial conditions to be retained in the mix-width at all times. The loss of transverse spectral information is demonstrated, however, along with the existence of a quasi-self-similar regime over short time intervals. Aspects of the IC's are shown to have a strong effect on the time to transition to the quasi-self-similar regime. With higher-dimensional blast waves, divergence restores the properties necessary for establishment of the self-similar state, but achieving it requires very high initial characteristic mode number and high Mach number for the incident blast wave. We point to recent stellar calculations that predict IC's we find incompatible with self-similarity, and
Energy Technology Data Exchange (ETDEWEB)
Miles, Aaron R. [Univ. of Maryland, College Park, MD (United States)
2004-01-01
In core-collapse supernovae, strong blast waves drive interfaces susceptible to Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) instabilities. In addition, perturbation growth can result from material expansion in large-scale velocity gradients behind the shock front. Laser-driven experiments are designed to produce a strongly shocked interface whose evolution is a scaled version of the unstable hydrogen-helium interface in core-collapse supernovae such as SN 1987A. The ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting transition to turbulence on supernovae observables that remain as yet unexplained. In this dissertation, we present a computational study of unstable systems driven by high Mach number shock and blast waves. Using multi-physics radiation hydrodynamics codes and theoretical models, we consider the late nonlinear instability evolution of single mode, few mode, and multimode interfaces. We rely primarily on 2D calculations but present recent 3D results as well. For planar multimode systems, we show that compressibility effects preclude the emergence of a regime of self-similar instability growth independent of the initial conditions (IC's) by allowing for memory of the initial conditions to be retained in the mix-width at all times. The loss of transverse spectral information is demonstrated, however, along with the existence of a quasi-self-similar regime over short time intervals. Aspects of the IC's are shown to have a strong effect on the time to transition to the quasi-self-similar regime. With higher-dimensional blast waves, divergence restores the properties necessary for establishment of the self-similar state, but achieving it requires very high initial characteristic mode number and high Mach number for the incident blast wave. We point to recent stellar calculations that predict IC's we find incompatible with self-similarity, and
Godfrey, Holly J.; Fry, Bill; Savage, Martha K.
2017-04-01
frequency range of 0.25-1 Hz. First-higher mode Love-waves are similarly slower than first-higher mode Rayleigh waves. This is incompatible with synthetic dispersion curves we calculate using isotropic, layered velocity models appropriate for Ruapehu and Tongariro, in which Love waves travel more quickly than Rayleigh waves of the same period. The Love-Rayleigh discrepancy is likely due to structures such as dykes or cracks in the vertical plane having increased influence on surface-wave propagation. However, several measurements at Ruapehu have Love-wave group velocities that are faster than Rayleigh-wave group velocities. The differences between the Love- and Rayleigh-wave dispersion curves also vary with the azimuth of the interstation path across Ruapehu and Tongariro Volcanoes. Significant azimuthal dependence of both Love and Rayleigh-wave velocities are also observed. This suggests azimuthal anisotropy within the volcanic structures, which coupled with radial anisotropy, makes the Vs structures of Ruapehu and Tongariro Volcanoes anisotropic with orthorhombic or lower order symmetry. We suggest that further work to determine three-dimensional volcanic structures should include provisions for such anisotropy.
Energy Technology Data Exchange (ETDEWEB)
Pennington, C.H.; Stenger, V.A.; Recchia, C.H.; Hahm, C.; Gorny, K.; Nandor, V. [Department of Physics, The Ohio State University, 174 West 18th Avenue, Columbus, Ohio 43210 (United States); Buffinger, D.R.; Lee, S.M.; Ziebarth, R.P. [Department of Chemistry, The Ohio State University, 120 West 18th Avenue, Columbus, Ohio 43210 (United States)
1996-02-01
Initial considerations lead one to suspect that effects of strong correlation might be present in the alkali fulleride superconductors. We report {ital direct} measurements of {sup 13}C {ital T}{sub 1} anisotropy at 80 K in Rb{sub 2}CsC{sub 60} and compare, in the context of the Korringa relation, the inferred spin-dipolar contribution to 1/{ital T}{sub 1} with the widths of the measured powder pattern line shape. The results demonstrate that the Korringa relation, valid in the limit of noninteracting electrons, holds in this case. Taken together with other normal-state NMR behavior this result makes important effects of strong correlation appear unlikely. {copyright} {ital 1996 The American Physical Society.}
Stoumpos, Constantinos C; Frazer, Laszlo; Clark, Daniel J; Kim, Yong Soo; Rhim, Sonny H; Freeman, Arthur J; Ketterson, John B; Jang, Joon I; Kanatzidis, Mercouri G
2015-06-03
The synthesis and properties of the hybrid organic/inorganic germanium perovskite compounds, AGeI3, are reported (A = Cs, organic cation). The systematic study of this reaction system led to the isolation of 6 new hybrid semiconductors. Using CsGeI3 (1) as the prototype compound, we have prepared methylammonium, CH3NH3GeI3 (2), formamidinium, HC(NH2)2GeI3 (3), acetamidinium, CH3C(NH2)2GeI3 (4), guanidinium, C(NH2)3GeI3 (5), trimethylammonium, (CH3)3NHGeI3 (6), and isopropylammonium, (CH3)2C(H)NH3GeI3 (7) analogues. The crystal structures of the compounds are classified based on their dimensionality with 1–4 forming 3D perovskite frameworks and 5–7 1D infinite chains. Compounds 1–7, with the exception of compounds 5 (centrosymmetric) and 7 (nonpolar acentric), crystallize in polar space groups. The 3D compounds have direct band gaps of 1.6 eV (1), 1.9 eV (2), 2.2 eV (3), and 2.5 eV (4), while the 1D compounds have indirect band gaps of 2.7 eV (5), 2.5 eV (6), and 2.8 eV (7). Herein, we report on the second harmonic generation (SHG) properties of the compounds, which display remarkably strong, type I phase-matchable SHG response with high laser-induced damage thresholds (up to ∼3 GW/cm(2)). The second-order nonlinear susceptibility, χS(2), was determined to be 125.3 ± 10.5 pm/V (1), (161.0 ± 14.5) pm/V (2), 143.0 ± 13.5 pm/V (3), and 57.2 ± 5.5 pm/V (4). First-principles density functional theory electronic structure calculations indicate that the large SHG response is attributed to the high density of states in the valence band due to sp-hybridization of the Ge and I orbitals, a consequence of the lone pair activation.
Institute of Scientific and Technical Information of China (English)
Feng Jing-Jing; Zhang Qi-Chang; Wang Wei
2011-01-01
In this paper,the extended Pad6 approximant is used to construct the homoclinic and the heteroclinic trajectories in nonlinear dynamical systems that are asymmetric at origin. Meanwhile,the conservative system,the autonomous systern,and the nonautonomous system equations with quadratic and cubic nonlinearities are considered. The disturbanceparameter εis not limited to being small. The ranges of the values of the linear and the nonlinear term parameters,which are variables,can be determined when the boundary values are satisfied. New conditions for the potentiality and the convergence are posed to make it possible to solve the boundary-value problems formulated for the orbitals and to evaluate the initial amplitude values.
Strong coupling between coherent gratings due to nonlinear spatial frequency mixing in Bi12SiO20
DEFF Research Database (Denmark)
Andersen, Peter E.; Buchhave, P.; Petersen, Paul Michael
1996-01-01
investigate the numerical calculations experimentally in a three-wave mixing setup and obtain good agreement between the experimental data and our predictions. Experimentally, we observe relative changes in the diffraction efficiency up to 500% due to nonlinear interactions between gratings...
Thermodynamic Measurement of Angular Anisotropy at the Hidden Order Transition of URu2 Si2
Trinh, Jennifer; Brück, Ekkes; Siegrist, Theo; Flint, Rebecca; Chandra, Premala; Coleman, Piers; Ramirez, Arthur P.
2016-10-01
The heavy fermion compound URu2 Si2 continues to attract great interest due to the unidentified hidden order it develops below 17.5 K. The unique Ising character of the spin fluctuations and low-temperature quasiparticles is well established. We present detailed measurements of the angular anisotropy of the nonlinear magnetization that reveal a cos4θ Ising anisotropy both at and above the ordering transition. With Landau theory, we show this implies a strongly Ising character of the itinerant hidden order parameter.
Galaxy clusters and microwave background anisotropy
Quilis, V; Sáez, D
1995-01-01
Previous estimates of the microwave background anisotropies produced by freely falling spherical clusters are discussed. These estimates are based on the Swiss-Cheese and Tolman-Bondi models. It is proved that these models give only upper limits to the anisotropies produced by the observed galaxy clusters. By using spherically symmetric codes including pressureless matter and a hot baryonic gas, new upper limits are obtained. The contributions of the hot gas and the pressureless component to the total anisotropy are compared. The effects produced by the pressure are proved to be negligible; hence, estimations of the cluster anisotropies based on N-body simulations are hereafter justified. After the phenomenon of violent relaxation, any realistic rich cluster can only produce small anisotropies with amplitudes of order 10^{-7}. During the rapid process of violent relaxation, the anisotropies produced by nonlinear clusters are expected to range in the interval (10^{-6},10^{-5}). The angular scales of these anis...
Liang Fei; Gao Hongjun
2011-01-01
Abstract In this paper, we consider the system of nonlinear viscoelastic equations u t t - Δ u + ∫ 0 t g 1 ( t - τ ) Δ u ( τ ) d τ - Δ u t = f 1 ( u , v ) , ( x , t ) ∈ Ω × ( 0 , T ) , v t t - Δ v + ∫ 0 t g 2 ( t - τ ) Δ v ( τ ) d τ - Δ v t = f 2 ( u , v ) , ( x , t ) ∈ Ω...
Institute of Scientific and Technical Information of China (English)
李银山; 刘波; 张明路; 段国林
2011-01-01
计及材料的非线性弹性,建立圆板自由振动的非线性动力学方程.采用Galerkin法,将圆板的非线性动力学偏微分方程简化成四种标准类型的二次非线性微分方程.提出一类强非线性动力系统的初值变换法,将描述动力系统的二阶常微分方程,化为以角频率、振幅和偏心距为独立变量的不完备非线性代数方程组,考虑初始条件补充约束方程,构成频率、振幅和偏心距为变量的完备非线性代数方程组.利用Maple程序可以方便地求解.结果表明,初值变换法不仅适合于对称振动问题,而且适合于非对称振动问题.首次给出二次非线性自由振动的偏一频曲线.%The nonlinear dynamic equation of free vibration of a circular plate is derived with nonlinear theory of elasticity. By using Calerkin' g method, the governing partial differential equation was reduced to four standard types of quadratic nonlinear ordinary ones. A method of initial-value transformation is presented for a class strongly nonlinear dynamic system. By using Ritz-Galerkin s method , an oscillation system governed by a set of second order ordinary differential equations, can be transformed into a set of incomplete non-linear algebraic equations with angular frequencies, amplitudes and central offsets as independent variables. Then, by supplement of some initial-value restrictions, the incomplete equations can be made complete, obtaining a set of non-linear algebraic equations with angular frequencies, amplitudes and central offsets, which can be solved conveniently by Maple program. Hie results show that the method of initial-value transformation can solve not only symmetry problems, but also asymmetry problems for free vibration. The offset-angular frequency backbone curves of quadratic nonlinear equations were presented for the first time.
Directory of Open Access Journals (Sweden)
Liang Fei
2011-01-01
Full Text Available Abstract In this paper, we consider the system of nonlinear viscoelastic equations u t t - Δ u + ∫ 0 t g 1 ( t - τ Δ u ( τ d τ - Δ u t = f 1 ( u , v , ( x , t ∈ Ω × ( 0 , T , v t t - Δ v + ∫ 0 t g 2 ( t - τ Δ v ( τ d τ - Δ v t = f 2 ( u , v , ( x , t ∈ Ω × ( 0 , T with initial and Dirichlet boundary conditions. We prove that, under suitable assumptions on the functions gi , fi (i = 1, 2 and certain initial data in the stable set, the decay rate of the solution energy is exponential. Conversely, for certain initial data in the unstable set, there are solutions with positive initial energy that blow up in finite time. 2000 Mathematics Subject Classifications: 35L05; 35L55; 35L70.
Magnetic Anisotropy in the Radula of Chiton
Institute of Scientific and Technical Information of China (English)
ZHAO Jian-Gao; QIAN Xia; LIU Wei; LIU Chuan-lin; ZHAN Wen-Shan
2000-01-01
Radular teeth of chitons were studied by using magnetic torque-meter and transmission electron microscopy (TEM). The magnetic torque curves give clear evidence of presence of strong uni-axial magnetic anisotropy. The easy axis is along the length direction of tongue-like radula. The TEM pattern shows that long chip-like magnetite nano-scaled particles packed in the radular teeth with both uni-axial shape anisotropy and magneto-crystalline anisotropy.
Magnetic Anisotropy in the Radula of Chiton
Zhao, Jian-Gao; Qian, Xia; Liu, Wei; Liu, Chuan-Lin; Zhan, Wen-Shan
2000-07-01
Radular teeth of chitons were studied by using magnetic torque-meter and transmission electron microscopy (TEM). The magnetic torque curves give clear evidence of presence of strong uni-axial magnetic anisotropy. The easy axis is along the length direction of tongue-like radula. The TEM pattern shows that long chip-like magnetite nano-scaled particles packed in the radular teeth with both uni-axial shape anisotropy and magneto-crystalline anisotropy.
Institute of Scientific and Technical Information of China (English)
YANG Jin; YU Wan-Lun; XIANG An-Ping
2006-01-01
We use Lewis-Riesenfeld invariant approach to treat the modified Jaynes-Cummings models involving any forms of nonlinearty of the bosonic field when strong boson-fermion couplings are nilpotent Grassmann valued. The general state functions, time evolution operator and the time-evolution expressions for both the bosonic number and the fermionic number are presented.
Directory of Open Access Journals (Sweden)
Kurt L. Polzin
2017-06-01
Full Text Available There is no theoretical underpinning that successfully explains how turbulent mixing is fed by wave breaking associated with nonlinear wave-wave interactions in the background oceanic internal wavefield. We address this conundrum using one-dimensional ray tracing simulations to investigate interactions between high frequency internal waves and inertial oscillations in the extreme scale separated limit known as “Induced Diffusion”. Here, estimates of phase locking are used to define a resonant process (a resonant well and a non-resonant process that results in stochastic jumps. The small amplitude limit consists of jumps that are small compared to the scale of the resonant well. The ray tracing simulations are used to estimate the first and second moments of a wave packet’s vertical wavenumber as it evolves from an initial condition. These moments are compared with predictions obtained from the diffusive approximation to a self-consistent kinetic equation derived in the ‘Direct Interaction Approximation’. Results indicate that the first and second moments of the two systems evolve in a nearly identical manner when the inertial field has amplitudes an order of magnitude smaller than oceanic values. At realistic (oceanic amplitudes, though, the second moment estimated from the ray tracing simulations is inhibited. The transition is explained by the stochastic jumps obtaining the characteristic size of the resonant well. We interpret this transition as an adiabatic ‘saturation’ process which changes the nominal background wavefield from supporting no mixing to the point where that background wavefield defines the normalization for oceanic mixing models.
Directory of Open Access Journals (Sweden)
D. A. Shcherbakova
2014-09-01
Full Text Available Supersonic shear wave imaging (SSI is a noninvasive, ultrasound-based technique to quantify the mechanical properties of bulk tissues by measuring the propagation speed of shear waves (SW induced in the tissue with an ultrasound transducer. The technique has been successfully validated in liver and breast (tumor diagnostics and is potentially useful for the assessment of the stiffness of arteries. However, SW propagation in arteries is subjected to different wave phenomena potentially affecting the measurement accuracy. Therefore, we assessed SSI in a less complex ex vivo setup, that is, a thick-walled and rectangular slab of an excised equine aorta. Dynamic uniaxial mechanical testing was performed during the SSI measurements, to dispose of a reference material assessment. An ultrasound probe was fixed in an angle position controller with respect to the tissue to investigate the effect of arterial anisotropy on SSI results. Results indicated that SSI was able to pick up stretch-induced stiffening of the aorta. SW velocities were significantly higher along the specimen's circumferential direction than in the axial direction, consistent with the circumferential orientation of collagen fibers. Hence, we established a first step in studying SW propagation in anisotropic tissues to gain more insight into the feasibility of SSI-based measurements in arteries.
Directory of Open Access Journals (Sweden)
Jiří Keller
Full Text Available Fractional anisotropy (FA is the most commonly used quantitative measure of diffusion in the brain. Changes in FA have been reported in many neurological disorders, but the implementation of diffusion tensor imaging (DTI in daily clinical practice remains challenging. We propose a novel color look-up table (LUT based on normative data as a tool for screening FA changes. FA was calculated for 76 healthy volunteers using 12 motion-probing gradient directions (MPG, a subset of 59 subjects was additionally scanned using 30 MPG. Population means and 95% prediction intervals for FA in the corpus callosum, frontal gray matter, thalamus and basal ganglia were used to create the LUT. Unique colors were assigned to inflection points with continuous ramps between them. Clinical use was demonstrated on 17 multiple system atrophy (MSA patients compared to 13 patients with Parkinson disease (PD and 17 healthy subjects. Four blinded radiologists classified subjects as MSA/non-MSA. Using only the LUT, high sensitivity (80% and specificity (84% were achieved in differentiating MSA subjects from PD subjects and controls. The LUTs generated from 12 and 30 MPG were comparable and accentuate FA abnormalities.
Keller, Jiří; Rulseh, Aaron M; Komárek, Arnošt; Latnerová, Iva; Rusina, Robert; Brožová, Hana; Vymazal, Josef
2013-01-01
Fractional anisotropy (FA) is the most commonly used quantitative measure of diffusion in the brain. Changes in FA have been reported in many neurological disorders, but the implementation of diffusion tensor imaging (DTI) in daily clinical practice remains challenging. We propose a novel color look-up table (LUT) based on normative data as a tool for screening FA changes. FA was calculated for 76 healthy volunteers using 12 motion-probing gradient directions (MPG), a subset of 59 subjects was additionally scanned using 30 MPG. Population means and 95% prediction intervals for FA in the corpus callosum, frontal gray matter, thalamus and basal ganglia were used to create the LUT. Unique colors were assigned to inflection points with continuous ramps between them. Clinical use was demonstrated on 17 multiple system atrophy (MSA) patients compared to 13 patients with Parkinson disease (PD) and 17 healthy subjects. Four blinded radiologists classified subjects as MSA/non-MSA. Using only the LUT, high sensitivity (80%) and specificity (84%) were achieved in differentiating MSA subjects from PD subjects and controls. The LUTs generated from 12 and 30 MPG were comparable and accentuate FA abnormalities.
Keller, Jiří; Rulseh, Aaron M.; Komárek, Arnošt; Latnerová, Iva; Rusina, Robert; Brožová, Hana; Vymazal, Josef
2013-01-01
Fractional anisotropy (FA) is the most commonly used quantitative measure of diffusion in the brain. Changes in FA have been reported in many neurological disorders, but the implementation of diffusion tensor imaging (DTI) in daily clinical practice remains challenging. We propose a novel color look-up table (LUT) based on normative data as a tool for screening FA changes. FA was calculated for 76 healthy volunteers using 12 motion-probing gradient directions (MPG), a subset of 59 subjects was additionally scanned using 30 MPG. Population means and 95% prediction intervals for FA in the corpus callosum, frontal gray matter, thalamus and basal ganglia were used to create the LUT. Unique colors were assigned to inflection points with continuous ramps between them. Clinical use was demonstrated on 17 multiple system atrophy (MSA) patients compared to 13 patients with Parkinson disease (PD) and 17 healthy subjects. Four blinded radiologists classified subjects as MSA/non-MSA. Using only the LUT, high sensitivity (80%) and specificity (84%) were achieved in differentiating MSA subjects from PD subjects and controls. The LUTs generated from 12 and 30 MPG were comparable and accentuate FA abnormalities. PMID:23990954
Strong third-order nonlinear response and optical limiting of α-NiMoO4 nanoparticles
Das, Amlan; Ratha, Satyajit; Yadav, Rajesh Kumar; Mondal, Anirban; Rout, Chandra Sekhar; Adarsh, K. V.
2017-07-01
In this manuscript, we demonstrate the strong resonant two photon absorption coefficient ≈71 ± 5 cm/GW at 532 nm in α-NiMoO4 nanoparticles prepared by a facile hydrothermal method. Strikingly, we have obtained the optical limiting onset threshold fluence (FON) of 36 mJ/cm2 for the linear transmittance of 0.64 with an excellent two photon absorption cross section (38 × 10-45 cm4 s), which suggests that they can be utilized as passive optical limiters. To explain the observed effects, we present a two-level rate equation model and numerically simulated the Z-scan peak shape, which is in good agreement with the experimental data. Further, we also show the normalized population density of the carriers in excited and ground states.
Energy Technology Data Exchange (ETDEWEB)
Szabó, Róbert; Ivezić, Željko; Kiss, László L.; Kolláth, Zoltán [Konkoly Observatory, MTA CSFK, Konkoly Thege Miklós út 15-17, H-1121 Budapest (Hungary); Jones, Lynne; Becker, Andrew C.; Davenport, James R. A. [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); Sesar, Branimir [Division of Physics, Mathematics and Astronomy, Caltech, Pasadena, CA 91125 (United States); Cutri, Roc M., E-mail: rszabo@konkoly.hu [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States)
2014-01-01
We present and discuss an extensive data set for the non-Blazhko ab-type RR Lyrae star SDSS J015450+001501, including optical Sloan Digital Sky Survey ugriz light curves and spectroscopic data, LINEAR and Catalina Sky Survey unfiltered optical light curves, and infrared Two Micron All Sky Survey (2MASS) JHK{sub s} and Wide-field Infrared Survey Explorer W1 and W2 light curves. Most notable is that light curves obtained by 2MASS include close to 9000 photometric measures collected over 3.3 yr and provide an exceedingly precise view of near-infrared variability. These data demonstrate that static atmosphere models are insufficient to explain multiband photometric light-curve behavior and present strong constraints for nonlinear pulsation models for RR Lyrae stars. It is a challenge to modelers to produce theoretical light curves that can explain data presented here, which we make publicly available.
Nonlinear control of high-frequency phonons in spider silk
Schneider, Dirk; Gomopoulos, Nikolaos; Koh, Cheong Y.; Papadopoulos, Periklis; Kremer, Friedrich; Thomas, Edwin L.; Fytas, George
2016-10-01
Spider dragline silk possesses superior mechanical properties compared with synthetic polymers with similar chemical structure due to its hierarchical structure comprised of partially crystalline oriented nanofibrils. To date, silk’s dynamic mechanical properties have been largely unexplored. Here we report an indirect hypersonic phononic bandgap and an anomalous dispersion of the acoustic-like branch from inelastic (Brillouin) light scattering experiments under varying applied elastic strains. We show the mechanical nonlinearity of the silk structure generates a unique region of negative group velocity, that together with the global (mechanical) anisotropy provides novel symmetry conditions for gap formation. The phononic bandgap and dispersion show strong nonlinear strain-dependent behaviour. Exploiting material nonlinearity along with tailored structural anisotropy could be a new design paradigm to access new types of dynamic behaviour.
Magnetization of superparamagnetics in the state of mechanical anisotropy
Ugulava, Archil; Chkhaidze, Simon; Kekutia, Shalva; Rostomashvili, Zurab
2015-01-01
The internal energy of magnetic anisotropy for some nanoparticles dominates over the thermal energy even at room temperature. Strong magnetic anisotropy of nanoparticles can significantly affect the process of magnetization of the magnetic fluid. This influence is substantial if the system of nanoparticles is in a state of mechanical anisotropy in which the anisotropy axes of the particles have the same direction. In this work, it is shown that the magnetization curve of the magnetic fluid in...
Romanowicz, Barbara; Wenk, Hans-Rudolf
2017-08-01
Seismic anisotropy has been found in many regions of the Earth's interior. Its presence in the Earth's crust has been known since the 19th century, and is due in part to the alignment of anisotropic crystals in rocks, and in part to patterns in the distribution of fractures and pores. In the upper mantle, seismic anisotropy was discovered 50 years ago, and can be attributed for the most part, to the alignment of intrinsically anisotropic olivine crystals during large scale deformation associated with convection. There is some indication for anisotropy in the transition zone, particularly in the vicinity of subducted slabs. Here we focus on the deep Earth - the lower mantle and core, where anisotropy is not yet mapped in detail, nor is there consensus on its origin. Most of the lower mantle appears largely isotropic, except in the last 200-300 km, in the D″ region, where evidence for seismic anisotropy has been accumulating since the late 1980s, mostly from shear wave splitting measurements. Recently, a picture has been emerging, where strong anisotropy is associated with high shear velocities at the edges of the large low shear velocity provinces (LLSVPs) in the central Pacific and under Africa. These observations are consistent with being due to the presence of highly anisotropic MgSiO3 post-perovskite crystals, aligned during the deformation of slabs impinging on the core-mantle boundary, and upwelling flow within the LLSVPs. We also discuss mineral physics aspects such as ultrahigh pressure deformation experiments, first principles calculations to obtain information about elastic properties, and derivation of dislocation activity based on bonding characteristics. Polycrystal plasticity simulations can predict anisotropy but models are still highly idealized and neglect the complex microstructure of polyphase aggregates with strong and weak components. A promising direction for future progress in understanding the origin of seismic anisotropy in the deep mantle
Terletska, Kateryna; Maderich, Vladimir; Brovchenko, Igor; Jung, Kyung Tae
2013-04-01
In the freshwater lakes in moderate latitudes stratification occurs as a result of the seasonal warming of the surface water layer. Than the intense wind surges (usually in autumn) tilt the surface and generate long basin-scale low-frequency standing internal waves (seiches). Depending on the initial interface tilt and stratification wide spectra of possible flow regimes can be observed [1]-[2].They varied from small amplitude symmetric seiches to large amplitude nonlinear waves.Nonlinearity leads to an asymmetry of internal waves and appearance of the surge or bore and further disintegration of it on a sequence of solitary waves. In present study degeneration of the strongly nonlinear internal seiches in elongated lakes with a concave "spoon-like" topography is investigated.Two different three-dimensional non-hydrostatic free-surface numerical models are used to investigate degeneration of large internal waves and its subsequent interaction with the concave lake slope. One of this model is non-hydrostatic model [3] and the other is a well-known MIT model. At first we consider idealized elongated elliptic-shape lake with the dimension of 5 km X 1 km with the maximal depth 30 m. The stratification in lake is assumed to be given in a form of the tangent function with a density difference between upper and lower layers 2 kgm-3 . It is assumed that motion in such lake is initiated by inclination of thermocline on a certain angle. Than lake adjusts to return to its original state producing internal seiches which begin interacting with a bottom topography. The process of degeneration of internal seiches in the lake with concave ends consist of chain of elementary processes: 1) steeping of long basin scale large amplitude wave, that evolve into internal surge, 2) surge interact with concave lake ends that leads the concentration of the flow and formation of down slope bottom jet along the lake axis, 3) due to cumulative effect local velocity in the jet accelerates up to
强非线性动力系统的频率增量法%FREQUENCY-INCREMENTAL METHOD FOR STRONGLY NONLINEAR DYNAMICAL SYSTEMS
Institute of Scientific and Technical Information of China (English)
黄彪; 宗国威; 陈兆莹; 胡敏
2001-01-01
Frequency is one of the essential factors to describe the dynamical property of the periodic oscillation systems. The strongly nonlinear problems are difficult to solve by the classical procedures such as perturbation methods. Their main limitation may be generally due to the unreasonable assumption of the constant frequency. The breakthrough point of a series of the results obtained over the years may be generally due to the instantaneity of the frequency. In a periodic oscillation, the periodic solutions can be expressed in the form of simple harmonics. Thus,an oscillation system which is described as a second order ordinary differential equation, can be expressed as an integral equation with phase angle as the independent variable and its first order derivative as a differential equation. Moreover, the integral equation problem is turned into the problem of solving a set of linear algebraic equations with the Fourier coefficients of the frequency increment as the independent variables using the principle of harmonic balance. The initial values of the incremental method are taken as the solutions of a conservative system. The amplitude and eccentricity are determined by the necessary condition for the existence of a periodic solution.When these algebraic equations are solved in an iterative way, a semi-analytical solution that satisfies any prescribed precision may be obtained. Two examples are given at end of this paper. In example one, the phase trajectories of van der Poi equation are computed for arbitrary values of the parameter ε＝ 1, 10,200, 1000. The result agrees very well with the numerical integration method even for ε＝ 1000. It is a good explanation for why the performance of the electron tube oscillators described by van der Poi 70 years ago is so stable. In example two, the periodic solutions and their bifurcations of a six-order nonlinear system are studied. The results are compared with the numerical integration method,and the agreements are
Modeling elastic anisotropy in strained heteroepitaxy
Krishna Dixit, Gopal; Ranganathan, Madhav
2017-09-01
Using a continuum evolution equation, we model the growth and evolution of quantum dots in the heteroepitaxial Ge on Si(0 0 1) system in a molecular beam epitaxy unit. We formulate our model in terms of evolution due to deposition, and due to surface diffusion which is governed by a free energy. This free energy has contributions from surface energy, curvature, wetting effects and elastic energy due to lattice mismatch between the film and the substrate. In addition to anisotropy due to surface energy which favors facet formation, we also incorporate elastic anisotropy due to an underlying crystal lattice. The complicated elastic problem of the film-substrate system subjected to boundary conditions at the free surface, interface and the bulk substrate is solved by perturbation analysis using a small slope approximation. This permits an analysis of effects at different orders in the slope and sheds new light on the observed behavior. Linear stability analysis shows the early evolution of the instability towards dot formation. The elastic anisotropy causes a change in the alignment of dots in the linear regime, whereas the surface energy anisotropy changes the dot shapes at the nonlinear regime. Numerical simulation of the full nonlinear equations shows the evolution of the surface morphology. In particular, we show, for parameters of the Ge0.25 Si0.75 on Si(0 0 1), the surface energy anisotropy dominates the shapes of the quantum dots, whereas their alignment is influenced by the elastic energy anisotropy. The anisotropy in elasticity causes a further elongation of the islands whose coarsening is interrupted due to facets on the surface.
Modeling elastic anisotropy in strained heteroepitaxy.
Dixit, Gopal Krishna; Ranganathan, Madhav
2017-09-20
Using a continuum evolution equation, we model the growth and evolution of quantum dots in the heteroepitaxial Ge on Si(0 0 1) system in a molecular beam epitaxy unit. We formulate our model in terms of evolution due to deposition, and due to surface diffusion which is governed by a free energy. This free energy has contributions from surface energy, curvature, wetting effects and elastic energy due to lattice mismatch between the film and the substrate. In addition to anisotropy due to surface energy which favors facet formation, we also incorporate elastic anisotropy due to an underlying crystal lattice. The complicated elastic problem of the film-substrate system subjected to boundary conditions at the free surface, interface and the bulk substrate is solved by perturbation analysis using a small slope approximation. This permits an analysis of effects at different orders in the slope and sheds new light on the observed behavior. Linear stability analysis shows the early evolution of the instability towards dot formation. The elastic anisotropy causes a change in the alignment of dots in the linear regime, whereas the surface energy anisotropy changes the dot shapes at the nonlinear regime. Numerical simulation of the full nonlinear equations shows the evolution of the surface morphology. In particular, we show, for parameters of the [Formula: see text] [Formula: see text] on Si(0 0 1), the surface energy anisotropy dominates the shapes of the quantum dots, whereas their alignment is influenced by the elastic energy anisotropy. The anisotropy in elasticity causes a further elongation of the islands whose coarsening is interrupted due to [Formula: see text] facets on the surface.
Institute of Scientific and Technical Information of China (English)
夏天; 孔繁超
2008-01-01
This paper proposes some regularity conditions.On the basis of the proposed regularity conditions,we show the strong consistency of maximum quasi-likelihood estimation (MQLE)in quasi-likelihood nonlinear models (QLNM).Our results may he regarded as a further generalization of the relevant results in Ref.[4].
Kastanya, Doddy Febrian
A Newton-BICGSTAB solver has been developed to reduce the CPU execution time of the FORMOSA-B boiling water reactor (BWR) core simulator. The new solver treats the strong non-linearities in the problem explicitly using the Newton's method, replacing the traditionally used nested iterative approach. Taking advantage of the higher convergence rate provided by the Newton's method, assuming that a good initial estimate of the unknowns is provided, and utilizing an efficient preconditioned BICGSTAB solver, we have developed a computationally efficient Newton-BICGSTAB solver to evaluate the three-dimensional, two-group neutron diffusion equations coupled with a two-phase flow model within a BWR core simulator. The robustness of the solver has been tested against numerous BWR core configurations and consistent results have been observed each time. The best exact Newton-BICGSTAB solver performance provides an overall speedup of 2.07 to the core simulator, with reference to the traditional approach, i.e. outer (fission-source)-inner (red/black line SOR). When solving the same problem using the traditional approach but with the BICGSTAB solver as the inner iteration solver [traditional (BICGSTAB)], we observed a speedup of 1.85. This means that the Newton-BICGSTAB solver provides an additional 12% increase in the overall speedup over the traditional (BICGSTAB) solver. However, one needs to note that, on average, the exact Newton-BICGSTAB solver provides an overall speedup of around 1.70; whereas, on average, the traditional (BICGSTAB) provides an overall speedup of around 1.60. An investigation on the feasibility of implementing an inexact Newton-BICGSTAB solver indicates that further reduction in the execution time can likely be obtained through this approach. This study shows that the inexact Newton-BICGSTAB solver can provide speedups of 1.73 to 2.10 with respect to the traditional solver.
Lin, Hua; Chen, Ling; Zhou, Liu-Jiang; Wu, Li-Ming
2013-08-28
Seven nonlinear optical (NLO) active selenides in the middle IR region, AX(II)4X(III)5Se12 (A = K(+)-Cs(+); X(II) = Mn(2+), Cd(2+); X(III) = Ga(3+), In(3+)) adopting the KCd4Ga5S12-type structure, have been synthesized by high-temperature solid-state reaction of an elemental mixture with ACl flux. Their three-dimensional network structures are stacked by M9Se24-layers of vertex sharing MSe4 tetrahedra, of which each center is jointly occupied by X(II) and X(III) atoms. Studies suggest that such tetrahedral building units can be regarded as the "multi-functional sites", on which the Cd(2+)/Ga(3+) pair gives rise to the coexistence of NLO and thermochromic properties, and the Mn(2+)/In(3+) pair leads to the coexistence of NLO and magnetic properties. The density functional theory (DFT) studies and the cutoff-energy-dependent NLO coefficient analyses reveal that such "multi-functional sites" contribute to the origin of the second harmonic generation (SHG) that is ascribed to the electronic transitions from the Se-4p states to the ns, np states of X(II) and X(III) atoms. Remarkably, title compounds show very strong SHG at an incident wavelength of 2.05 μm, roughly 16-40 times that of commercial AgGaS2; among them, ACd4In5Se12 (A = Rb, Cs) represents the strongest SHG among chalcogenides to date.
Anisotropy of rare-earth magnets
Institute of Scientific and Technical Information of China (English)
R.Skomski; D.J.Sellmyer
2009-01-01
Rare-earth intermetallics such as Nd2FeI4B and Sm-Co are widely used as high-performance permanent magnets,because they combine high magnetocrystalline anisotropy with reasonable magnetization and Curie temperature.The anisotropy is a combined effect of spin-orbit coupling and electrostatic crystal-field interactions.The main contribution comes from the rare-earth 4f electrons,which are well-screened from the crystalline environment but exhibit a strong spin-orbit coupling.In this limit,the magnetocrystalline anisotropy has a very transparent physical interpretation,the anisotropy energy essentially being equal to the energy of Hund's-rules 4f ion in the crystal field.The corresponding expression for the lowest-order uniaxial anisotropy constant K1 is used to discuss rare-earth substitutions,which have recently attracted renewed interest due to shifts in the rare-earth production and demand.Specific phenomena reviewed in this article are the enhancement of the anisotropy of Sm2Fe17 due to interstitial nitrogen,the use of Sm-Co magnets for high-temperature applications,and the comparison of rare-earth single-ion anisotropy with other single-ion and two-ion mechanisms.
The variation of linewidth in exchange coupled bilayer films with stress anisotropy
Energy Technology Data Exchange (ETDEWEB)
Zhang, Lei [Inner Mongolia Key Lab of Nanoscience and Nanotechnology and School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021 (China); Rong, Jianhong, E-mail: jhrong502@163.com [Inner Mongolia Key Lab of Nanoscience and Nanotechnology and School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021 (China); Yun, Guohong, E-mail: ndghyun@imu.edu.cn [Inner Mongolia Key Lab of Nanoscience and Nanotechnology and School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021 (China); College of Physics and Electronic Information, Inner Mongolia Normal University, Hohhot 010022 (China); Wang, Dong; Bao, Lingbo [Inner Mongolia Key Lab of Nanoscience and Nanotechnology and School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021 (China)
2016-12-01
The frequency linewidth and the field linewidth in ferromagnetic/antiferromagnetic bilayer films with stress anisotropy have been investigated by using ferromagnetic resonance method. The effects of the stress anisotropy for in-plane anisotropy, weak and strong perpendicular anisotropy on linewidth are observed. It is found that the frequency and the field linewidth all increase for in-plane and weak perpendicular anisotropy, as the stress anisotropy field increases. And furthermore, the stress anisotropy field affects obviously the frequency and the field linewidth for unsaturation field.
Fabrication of electrodeposited Co nanowire arrays with perpendicular anisotropy
Energy Technology Data Exchange (ETDEWEB)
Ge Shihui E-mail: zhangzz@lzu.edu.cn; Ma Xiao; Li Chao; Li Wei
2001-05-01
Co nanowire arrays have been electrodeposited into polycarbonate membranes with nanosized pores at different voltages. By means of X-ray diffraction, electron diffraction, vibrating sample magnetometer, their microstructures and magnetic properties were investigated at full length. The sample prepared at -1.2 V, 250 mA/cm{sup 2} shows perpendicular anisotropy, but the one deposited at -1.0V, 125 mA/cm{sup 2} has no perpendicular anisotropy. This different magnetic behavior can be explained from their different microstructures. X-ray diffraction and electron diffraction evidence that the former sample is amorphous, and the latter is polycrystalline. In the polycrystalline sample, due to the competition of shape anisotropy and magnetocrystal anisotropy, the sample does not display perpendicular anisotropy. But magnetocrystal anisotropy is very small in amorphous sample, therefore, shape anisotropy plays a dominant role which leads to strong perpendicular anisotropy because of shape anisotropy. Furthermore, applying a magnetic field during deposition, Co grains will preferentially grow with c-axis along the wire axis, which also leads to strong perpendicular anisotropy.
Goryachev, Maxim; Galliou, Serge; Tobar, Michael E
2015-01-01
A system consisting of a SQUID amplifier coupled to a Bulk Acoustic Wave resonator is investigated experimentally from the small to large signal regimes. Both parallel and series connection topologies of the system are verified. The study reveals significant non-Duffing response that is associated with the nonlinear characteristics of Josephson junctions. The nonlinearity provides quasi-periodic structure of the spectrum in both incident power and frequency. The result gives an insight into the open loop behaviour of a future Cryogenic Quartz Oscillator operating with a SQUID amplifier as the active device.
Supernovae anisotropy power spectrum
Ghodsi, Hoda; Habibi, Farhang
2016-01-01
We contribute another anisotropy study to this field of research using Supernovae Type Ia (SNe Ia). In this work, we utilise the power spectrum calculation method and apply it to both the current SNe Ia data and simulation. Our simulations are constructed with the characteristics of the upcoming survey of the Large Synoptic Survey Telescope (LSST), which shall bring us the largest SNe Ia collection to date. We make predictions for the amplitude of a possible dipole anisotropy or anisotropy in higher multipole moments that would be detectable by the LSST.
Texture induced microwave background anisotropies
Energy Technology Data Exchange (ETDEWEB)
Borrill, Julian; Copeland, Edmund J.; Liddle, Andrew R.; Stebbins, Albert; Veeraraghavan, Shoba
1994-03-01
We use numerical simulations to calculate the cosmic microwave background anisotropy induced by the evolution of a global texture field, with special emphasis on individual textures. Both spherically symmetric and general configurations are analyzed, and in the latter case we consider field configurations which exhibit unwinding events and also ones which do not. We compare the results given by evolving the field numerically under both the expanded core (XCORE) and non-linear sigma model (NLSM) approximations with the analytic predictions of the NLSM exact solution for a spherically symmetric self-similar (SSSS) unwinding. We find that the random unwinding configuration spots' typical peak height is 60-75\\% and angular size typically only 10% of those of the SSSS unwinding, and that random configurations without an unwinding event nonetheless may generate indistinguishable hot and cold spots. A brief comparison is made with other work.
Troxel, M A; Peel, Austin
2013-01-01
The study of relativistic, higher order and nonlinear effects has become necessary in recent years in the pursuit of precision cosmology. We develop and apply here a framework to study gravitational lensing in exact models in general relativity that are not restricted to homogeneity and isotropy, and where full nonlinearity and relativistic effects are included. We apply the framework to a specific, anisotropic galaxy cluster model which is based on a modified NFW halo density profile and described by the Szekeres metric. We examine the effects of increasing levels of anisotropy in the galaxy cluster on lensing observables like the convergence and shear for various lensing geometries, finding a strong nonlinear response in both the convergence and shear for rays passing through anisotropic regions of the cluster. Deviation from the expected values in a spherically symmetric structure are asymmetric with respect to path direction and thus will persist as a statistical effect when averaged over some ensemble of...
Heterogeneity and anisotropy of Earth's inner core
Deuss, Arwen
2014-01-01
Seismic observations provide strong evidence that Earth's inner core is anisotropic, with larger velocity in the polar than in the equatorial direction. The top 60-80 km of the inner core is isotropic; evidence for an innermost inner core is less compelling. The anisotropy is most likely due to alig
Heterogeneity and anisotropy of Earth's inner core
Deuss, Arwen
2014-01-01
Seismic observations provide strong evidence that Earth's inner core is anisotropic, with larger velocity in the polar than in the equatorial direction. The top 60-80 km of the inner core is isotropic; evidence for an innermost inner core is less compelling. The anisotropy is most likely due to
Spin Wave Theory of Strongly Anisotropic Magnets
DEFF Research Database (Denmark)
Lindgård, Per-Anker
1977-01-01
A strong anisotropy gives rise to a non-spherical precession of the spins with different amplitudes in the x and y directions. The highly anharmonic exchange interaction thereby becomes effectively anisotropic. The possibility of detecting a genuine two-ion anisotropy is discussed, and comments a...
Coexistence of weak and strong wave turbulence in incompressible Hall MHD
Meyrand, Romain; Kiyani, Khurom; Galtier, Sebastien
2016-04-01
We report a numerical investigation of 3D Hall Magnetohydrodynamic turbulence with a strong mean magnetic field. By using a helicity decomposition and a cross-bicoherence analysis, we observe that the nonlinear 3-wave coupling is substantial among ion cyclotron and whistler waves. By studying in detail the degree of nonlinearity of these two populations we show that ion cyclotron and whistler turbulent fluctuations belong respectively to strong and weak wave turbulence. The non trivial blending of these two regime give rise to anomalous anisotropy and scaling properties. The separation of the weak random wave and strong coherent turbulence component can however be effectively done using simultaneous space and time Fourier transforms. Using this techniques we show that it is possible to recover some statistical prediction of weak turbulent theory.
Bidault, Sébastien; Brasselet, Sophie; Zyss, Joseph; Maury, Olivier; Le Bozec, Hubert
2007-01-01
Following on the recent experimental demonstration of a discrepancy between the nonlinear optical (NLO) behavior of several π-conjugated chromophores and their assumed octupolar symmetry, the authors investigate how geometrical distortions influence the NLO response of multipolar push-pull molecules. Their analytical model is set on a basis of valence-bond and charge-transfer states to estimate the hyperpolarizability of organic and metallo-organic chromophores using the lowest possible number of variables. Since symmetry breakdown changes the definition of the molecular Cartesian framework, tensorial spherical coordinates are implemented. The evolution of the nonlinear molecular anisotropy with possible rotational deviations is then evaluated for two recently studied chromophores. Zero-frequency calculations show that, outside optical resonance, weak geometrical distortions lead to strong anisotropy variations in agreement with experimental data. Their goal is to underscore which molecular engineering strategies should be applied when designing a photoisomerizable nonlinear octupole.
Computing magnetic anisotropy constants of single molecule magnets
Indian Academy of Sciences (India)
S Ramasesha; Shaon Sahoo; Rajamani Raghunathan; Diptiman Sen
2009-09-01
We present here a theoretical approach to compute the molecular magnetic anisotropy parameters, and for single molecule magnets in any given spin eigenstate of exchange spin Hamiltonian. We first describe a hybrid constant -valence bond (VB) technique of solving spin Hamiltonians employing full spatial and spin symmetry adaptation and we illustrate this technique by solving the exchange Hamiltonian of the Cu6Fe8 system. Treating the anisotropy Hamiltonian as perturbation, we compute the and values for various eigenstates of the exchange Hamiltonian. Since, the dipolar contribution to the magnetic anisotropy is negligibly small, we calculate the molecular anisotropy from the single-ion anisotropies of the metal centers. We have studied the variation of and by rotating the single-ion anisotropies in the case of Mn12Ac and Fe8 SMMs in ground and few low-lying excited states of the exchange Hamiltonian. In both the systems, we find that the molecular anisotropy changes drastically when the single-ion anisotropies are rotated. While in Mn12Ac SMM values depend strongly on the spin of the eigenstate, it is almost independent of the spin of the eigenstate in Fe8 SMM. We also find that the value is almost insensitive to the orientation of the anisotropy of the core Mn(IV) ions. The dependence of on the energy gap between the ground and the excited states in both the systems has also been studied by using different sets of exchange constants.
Anisotropy of transport in bulk Rashba metals
Brosco, Valentina; Grimaldi, Claudio
2017-05-01
The recent experimental discovery of three-dimensional (3D) materials hosting a strong Rashba spin-orbit coupling calls for the theoretical investigation of their transport properties. Here we study the zero-temperature dc conductivity of a 3D Rashba metal in the presence of static diluted impurities. We show that, at variance with the two-dimensional case, in 3D systems, spin-orbit coupling affects dc charge transport in all density regimes. We find in particular that the effect of spin-orbit interaction strongly depends on the direction of the current, and we show that this yields strongly anisotropic transport characteristics. In the dominant spin-orbit coupling regime where only the lowest band is occupied, the conductivity anisotropy is governed entirely by the anomalous component of the renormalized current. We propose that measurements of the conductivity anisotropy in bulk Rashba metals may give a direct experimental assessment of the spin-orbit strength.
Predicted Impacts of Proton Temperature Anisotropy on Solar Wind Turbulence
Klein, Kristopher G
2015-01-01
Particle velocity distributions measured in the weakly collisional solar wind are frequently found to be non-Maxwellian, but how these non-Maxwellian distributions impact the physics of plasma turbulence in the solar wind remains unanswered. Using numerical solutions of the linear dispersion relation for a collisionless plasma with a bi-Maxwellian proton velocity distribution, we present a unified framework for the four proton temperature anisotropy instabilities, identifying the associated stable eigenmodes, highlighting the unstable region of wavevector space, and presenting the properties of the growing eigenfunctions. Based on physical intuition gained from this framework, we address how the proton temperature anisotropy impacts the nonlinear dynamics of the \\Alfvenic fluctuations underlying the dominant cascade of energy from large to small scales and how the fluctuations driven by proton temperature anisotropy instabilities interact nonlinearly with each other and with the fluctuations of the large-scal...
Azimuthal anisotropy measurements by STAR
Energy Technology Data Exchange (ETDEWEB)
Yi, Li
2014-06-15
The recent study of centrality and transverse momentum (p{sub T}) dependence of inclusive charged hardron elliptic anisotropy (v{sub 2}) at midrapidity (|η|<1.0) in Au+Au collision at √(s{sub NN})=7.7,11.5,19.6,27, and39 GeV in STAR Beam Energy Scan program is presented. We show that the observed increase of inclusive v{sub 2} is mainly due to the average p{sub T} increase with energy. In Au+Au 200 GeV collisions, the triangular anisotropy (v{sub 3}) measurements highly depend on measurement methods; v{sub 3} is strongly dependent on Δη. The difference between two- and four-particle cumulants v{sub 2}{2} and v{sub 2}{4} for Au+Au and Cu+Cu collision at √(s{sub NN})=62.4 and 200 GeV is used to explore flow fluctuations. Furthermore, by exploiting the symmetry of average flow in pseudorapidity η about midrapidity, the Δη-dependent and independent components are separated using v{sub 2}{2} and v{sub 2}{4}.
Predicted impacts of proton temperature anisotropy on solar wind turbulence
Energy Technology Data Exchange (ETDEWEB)
Klein, K. G., E-mail: kristopher.klein@unh.edu [Space Science Center, University of New Hampshire, Durham, New Hampshire 03824 (United States); Howes, G. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)
2015-03-15
Particle velocity distributions measured in the weakly collisional solar wind are frequently found to be non-Maxwellian, but how these non-Maxwellian distributions impact the physics of plasma turbulence in the solar wind remains unanswered. Using numerical solutions of the linear dispersion relation for a collisionless plasma with a bi-Maxwellian proton velocity distribution, we present a unified framework for the four proton temperature anisotropy instabilities, identifying the associated stable eigenmodes, highlighting the unstable region of wavevector space and presenting the properties of the growing eigenfunctions. Based on physical intuition gained from this framework, we address how the proton temperature anisotropy impacts the nonlinear dynamics of the Alfvénic fluctuations underlying the dominant cascade of energy from large to small scales and how the fluctuations driven by proton temperature anisotropy instabilities interact nonlinearly with each other and with the fluctuations of the large-scale cascade. We find that the nonlinear dynamics of the large-scale cascade is insensitive to the proton temperature anisotropy and that the instability-driven fluctuations are unlikely to cause significant nonlinear evolution of either the instability-driven fluctuations or the turbulent fluctuations of the large-scale cascade.
Predicted impacts of proton temperature anisotropy on solar wind turbulence
Klein, K. G.; Howes, G. G.
2015-03-01
Particle velocity distributions measured in the weakly collisional solar wind are frequently found to be non-Maxwellian, but how these non-Maxwellian distributions impact the physics of plasma turbulence in the solar wind remains unanswered. Using numerical solutions of the linear dispersion relation for a collisionless plasma with a bi-Maxwellian proton velocity distribution, we present a unified framework for the four proton temperature anisotropy instabilities, identifying the associated stable eigenmodes, highlighting the unstable region of wavevector space and presenting the properties of the growing eigenfunctions. Based on physical intuition gained from this framework, we address how the proton temperature anisotropy impacts the nonlinear dynamics of the Alfvénic fluctuations underlying the dominant cascade of energy from large to small scales and how the fluctuations driven by proton temperature anisotropy instabilities interact nonlinearly with each other and with the fluctuations of the large-scale cascade. We find that the nonlinear dynamics of the large-scale cascade is insensitive to the proton temperature anisotropy and that the instability-driven fluctuations are unlikely to cause significant nonlinear evolution of either the instability-driven fluctuations or the turbulent fluctuations of the large-scale cascade.
ANISOTROPY DETERMINATIONS IN EXCHANGE SPRING MAGNETS.
Energy Technology Data Exchange (ETDEWEB)
LEWIS,L.H.; HARLAND,C.L.
2002-08-18
Ferromagnetic nanocomposites, or ''exchange spring'' magnets, possess a nanoscaled microstructure that allows intergrain magnetic exchange forces to couple the constituent grains and alter the system's effective magnetic anisotropies. While the effects of the anisotropy alterations are clearly seen in macroscopic magnetic measurement, it is extremely difficult to determine the detailed effects of the system's exchange coupling, such as the interphase exchange length, the inherent domain wall widths or the effective anisotropies of the system. Clarification of these materials parameters may be obtained from the ''micromagnetic'' phenomenological model, where the assumption of magnetic reversal initiating in the magnetically-soft regions of the exchange-spring maqet is explicitly included. This approach differs from that typically applied by other researchers and allows a quantitative estimate of the effective anisotropies of an exchange spring system. Hysteresis loops measured on well-characterized nanocomposite alloys based on the composition Nd{sub 2}Fe{sub 14}B + {alpha}-Fe at temperatures above the spin reorientation temperature were analyzed within the framework of the micromagnetic phenomenological model. Preliminary results indicate that the effective anisotropy constant in the material is intermediate to that of bulk {alpha}-Fe and bulk Nd{sub 2}Fe{sub 14}B and increases with decreasing temperature. These results strongly support the idea that magnetic reversal in nanocomposite systems initiates in the lower-anisotropy regions of the system, and that the soft-phase regions become exchange-hardened by virtue of their proximity to the magnetically-hard regions.
Anisotropy of ice Ih: Developement of fabric and effects of anisotropy on deformation
Thorsteinsson, Throstur
The anisotropy arising from preferred crystal orientation of ice I h is examined. To understand plastic anisotropy of polycrystalline materials it is necessary to examine the behavior at the single crystal level. Ice crystals have extremely strong plastic anisotropy that strongly influences the bulk behavior. There are several ways to relate single crystal deformation to the bulk behavior. Two approaches are used here. The first one is to assume a homogeneous stress throughout the bulk, which allows us to derive analytical relations between stress and strain rate. The anisotropy affects the strain rate-stress relationship significantly. For example strongly anisotropic ice, with a vertically symmetric fabric, can deform transversely to the applied stress in pure shear, be nearly undeformable in vertical compression, and shear easily in simple shear. The second approach takes the interaction between neighboring crystals into account, and recrystallization processes are also considered. Comparison of fabric evolution using the model and fabric from the GRIP ice core indicates that nearest neighbor interaction is necessary to explain observations. Quantification of the interaction is complicated by recrystallization processes. A consistent method of characterizing measured fabric is needed to verify models of fabric development. Here the elastic anisotropy of ice plays a central role, and relations between fabric and elastic wave velocities are used to characterize fabric. As always, several other methods are possible, but comparison indicates that sonic measurements give an accurate estimate for deformation effects from vertically symmetric fabric especially in simple shear. The deformation of the borehole at Dye 3, Greenland, has been measured with borehole inclinometry. Sonic velocity measurements done in the borehole allow us to model the deformation using an anisotropic flow law. Anisotropy alone cannot explain all the deformation. The additional processes
Energy Technology Data Exchange (ETDEWEB)
Yin, Hongyao [Department of Chemistry, Shanghai Normal University, Shanghai 200234 (China); Xiao, Haibo, E-mail: xiaohb@shnu.edu.cn [Department of Chemistry, Shanghai Normal University, Shanghai 200234 (China); Ding, Lei [Department of Chemistry, Shanghai Normal University, Shanghai 200234 (China); Zhang, Chun; Ren, Aiming [State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023 (China); Li, Bo [Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200241 (China)
2015-02-01
A spirobifluorene-bridged donor/donor chromophore, 2,7-bis-(4-(N,N-diphenylamino)phen-1-yl)-9,9′-spirobifluorene (SPF-TP), was found to combine excellent transparency in the near UV–visible region (λ{sub cut-off} ≤ 420 nm), large two-photon absorption cross-section (4.5 × 10{sup 3}GM) and high thermal stability (T{sub d} = 501 °C). In comparison to the reported two-photon absorption molecules, SPF-TP represents the best thermal stability so far described in the literature. The main electronic factors explaining the high two-photon absorption activities of SPF-TP were analyzed by theoretical calculations. Cyclic voltammograms were employed to explore the causes of the excellent transparency of SPF-TP. It was found that the spiroconjugation effect is responsible for the excellent nonlinearity/transparency/thermal stability trade-off in SPF-TP. In addition, SPF-TP is also a good two-photon induced blue fluorescent material with high fluorescence quantum yield (Φ = 0.90, in THF). - Highlights: • We report a molecule exhibiting excellent transparency. • The two-photon absorption cross-section is as large as 4.5 × 10{sup 3}GM. • The molecule exhibits excellent thermal stability. • The molecule is a good two-photon induced blue fluorescent material. • The spiroconjugation effect explains the excellent properties.
Energy Technology Data Exchange (ETDEWEB)
Okuzumi, Satoshi [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan); Inutsuka, Shu-ichiro, E-mail: okuzumi@geo.titech.ac.jp [Department of Physics, Nagoya University, Nagoya, Aichi 464-8602 (Japan)
2015-02-10
The ionization state of the gas plays a key role in the magnetohydrodynamics (MHD) of protoplanetary disks. However, the ionization state can depend on the gas dynamics, because electric fields induced by MHD turbulence can heat up plasmas and thereby affect the ionization balance. To study this nonlinear feedback, we construct an ionization model that includes plasma heating by electric fields and impact ionization by heated electrons, as well as charging of dust grains. We show that when plasma sticking onto grains is the dominant recombination process, the electron abundance in the gas decreases with increasing electric field strength. This is a natural consequence of electron-grain collisions whose frequency increases with the electron's random velocity. The decreasing electron abundance may lead to a self-regulation of MHD turbulence. In some cases, not only the electron abundance but also the electric current decreases with increasing field strength in a certain field range. The resulting N-shaped current-field relation violates the fundamental assumption of the non-relativistic MHD that the electric field is uniquely determined by the current density. At even higher field strengths, impact ionization causes an abrupt increase of the electric current as expected by previous studies. We find that this discharge current is multi-valued (i.e., the current-field relation is S-shaped) under some circumstances, and that the intermediate branch is unstable. The N/S-shaped current-field relations may yield hysteresis in the evolution of MHD turbulence in some parts of protoplanetary disks.
Gowtham, P. G.; Stiehl, G. M.; Ralph, D. C.; Buhrman, R. A.
2016-01-01
We report measurements of the in-plane magnetoelastic coupling in both as-deposited and annealed ultrathin Ta/CoFeB/MgO layers as a function of uniaxial strain, conducted using a four-point bending apparatus. While as-deposited samples show only a weak dependence of the magnetoelastic coupling on the CoFeB layer thickness in the ultrathin regime (<2 nm ) , we observe the onset of a strong thickness dependence upon annealing. This dependence can be modeled as arising from a combination of effective surface and volume contributions to the magnetoelastic coupling. We point out that if similar thickness dependence exists for magnetoelastic coupling in response to biaxial strain, then the standard Néel model for the magnetic anisotropy energy acquires a term inversely proportional to the magnetic layer thickness. This contribution can significantly change the overall magnetic anisotropy, and provides a natural explanation for the strongly nonlinear dependence of magnetic anisotropy energy on magnetic layer thickness that is commonly observed for ultrathin annealed CoFeB/MgO films with perpendicular magnetic anisotropy.
Yamada, Hirofumi
2012-01-01
Based on the strong coupling expansion, we reinvestigate the scaling behavior of the susceptibility chi of two-dimensional O(N) sigma model on the square lattice by the use of Pade-Borel approximants. To exploit the Borel transform, we express the bare coupling g in series expansion in chi. At large N, Pade-Borel approximants exhibit the scaling behavior at the four-loop level. Then, the estimation of the non-perturbative constant associated with the susceptibility is performed for N>=3 and the results are compared with the available theoretical results and Monte Carlo data.
STUDYING THE INTERSTELLAR MAGNETIC FIELD FROM ANISOTROPIES IN VELOCITY CHANNELS
Energy Technology Data Exchange (ETDEWEB)
Esquivel, A. [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70-543, 04510 México D.F., México (Mexico); Lazarian, A. [Astronomy Department, University of Wisconsin–Madison, 475 N. Charter Street, Madison, WI (United States); Pogosyan, D., E-mail: esquivel@nucleares.unam.mx, E-mail: lazarian@astro.wisc.edu, E-mail: pogosyan@ualberta.ca [Physics Department, University of Alberta, Edmonton, AB (Canada)
2015-11-20
Turbulence in the interstellar medium is anisotropic due to the ubiquitous magnetic fields. This anisotropy depends on the strength of the magnetic field and leaves an imprint on observations of spectral line maps. We use a grid of ideal magnetohydrodynamic simulations of driven turbulence and produce synthetic position–position–velocity maps to study the turbulence anisotropy in velocity channels of various resolutions. We found that the average structure function of velocity channels is aligned with the projection of the magnetic field on the plane of the sky. We also found that the degree of such anisotropy increases with the magnitude of the magnetic field. For thick velocity channels (low velocity resolution), the anisotropy is dominated by density, and the degree of anisotropy in these maps allows one to distinguish sub-Alfvénic and super-Alfvénic turbulence regimes, but it also depends strongly on the sonic Mach number. For thin channels (high velocity resolution), we find that the anisotropy depends less on the sonic Mach number. An important limitation of this technique is that it only gives a lower limit on the magnetic field strength because the anisotropy is related only to the magnetic field component on the plane of the sky. It can, and should, be used in combination with other techniques to estimate the magnetic field, such as the Fermi-Chandrasekhar method, anisotropies in centroids, Faraday rotation measurements, or direct line-of-sight determinations of the field from Zeeman effect observations.
Dong, Yitong; Son, Dong Hee
2015-01-02
The dependence of the energy transfer rate on the content of sp(2)-hybridized carbon atoms in the hybrid structures of reduced graphene oxide (RGO) and Mn-doped quantum dot (QD(Mn)) was investigated. Taking advantage of the sensitivity of QD(Mn)'s dopant luminescence lifetime only to the energy transfer process without interference from the charge transfer process, the correlation between the sp(2) carbon content in RGO and the rate of energy transfer from QD(Mn) to RGO was obtained. The rate of energy transfer showed a strongly superlinear increase with increasing sp(2) carbon content in RGO, suggesting the possible cooperative behavior of sp(2) carbon domains in the energy transfer process as the sp(2) carbon content increases.
Texture induced magnetic anisotropy in Fe3O4 films
Liu, Er; Huang, Zhaocong; Zheng, Jian-Guo; Yue, Jinjin; Chen, Leyi; Wu, Xiumei; Sui, Yunxia; Zhai, Ya; Tang, Shaolong; Du, Jun; Zhai, Hongru
2015-10-01
This letter reports a free energy density model for textured films in which the related physical concept and expression of magneto-texture anisotropy energy are presented. The structural characterization and out-of-plane angular dependence ferromagnetic resonance of strongly textured Fe3O4 films were systematically investigated. We found that the typical free energy density model for polycrystalline film cannot be applied to the textured films. With the introduction of magneto-texture anisotropy energy in the free energy density model for thin films, we simulated and quantitatively determined the competing anisotropies in (111)-textured Fe3O4 films.
Institute of Scientific and Technical Information of China (English)
王学文; 王华兰; 王成
2009-01-01
A family of higher-order solitons called elegant Hermite Gaussian higher-order soliton (EHGHOS) in the strongly nonlocal nonlinear media is introduced.The transverse distribution of EHGHOS at the entrance plane is the same as the waist of elegant Hermite Gaussian beam.And it presents as periodical evolution with the period Δz=π/β0when propagates.%本文得到了强非局域非线性介质中的一类高阶空间孤子,即完美厄米高斯高阶孤子.此类高阶孤子在入射面处的场分布与完美厄米高斯光束束腰处的场分布相同.在传输过程中,其场分布呈周期性演化,周期为Δz=π/β0.
Laboratory measurements of the viscous anisotropy of olivine aggregates.
Hansen, L N; Zimmerman, M E; Kohlstedt, D L
2012-12-20
A marked anisotropy in viscosity develops in Earth's mantle as deformation strongly aligns the crystallographic axes of the individual grains that comprise the rocks. On the basis of geodynamic simulations, processes significantly affected by viscous anisotropy include post-glacial rebound, foundering of lithosphere and melt production above subduction zones. However, an estimate of the magnitude of viscous anisotropy based on the results of deformation experiments on single crystals differs by three orders of magnitude from that obtained by grain-scale numerical models of deforming aggregates with strong crystallographic alignment. Complicating matters, recent experiments indicate that deformation of the uppermost mantle is dominated by dislocation-accommodated grain-boundary sliding, a mechanism not activated in experiments on single crystals and not included in numerical models. Here, using direct measurements of the viscous anisotropy of highly deformed polycrystalline olivine, we demonstrate a significant directional dependence of viscosity. Specifically, shear viscosities measured in high-strain torsion experiments are 15 times smaller than normal viscosities measured in subsequent tension tests performed parallel to the torsion axis. This anisotropy is approximately an order of magnitude larger than that predicted by grain-scale simulations. These results indicate that dislocation-accommodated grain-boundary sliding produces an appreciable anisotropy in rock viscosity. We propose that crystallographic alignment imparts viscous anisotropy because the rate of deformation is limited by the movement of dislocations through the interiors of the crystallographically aligned grains. The maximum degree of anisotropy is reached at geologically low shear strain (of about ten) such that deforming regions of the upper mantle will exhibit significant viscous anisotropy.
Crustal radial anisotropy beneath Cameroon from ambient noise tomography
Ojo, Adebayo Oluwaseun; Ni, Sidao; Li, Zhiwei
2017-01-01
To increase the understanding of crustal deformation and crustal flow patterns due to tectonic processes in Cameroon, we study the lateral variability of the crustal isotropic velocity and radial anisotropy estimated using Ambient Noise Tomography (ANT). Rayleigh and Love wave Noise Correlation Functions (NCFs) were retrieved from the cross-correlation of seismic ambient noise data recorded in Cameroon, and phase velocities at periods of 8 to 30 s were measured to perform surface wave tomography. Joint inversion of Rayleigh and Love wave data for isotropic velocity models could not fit the observed dispersions simultaneously. We attribute the Love-Rayleigh discrepancy to the presence of radial anisotropy in the crust and estimated its magnitude. Our 3-D radial anisotropic model reveals the spatial variation of strong to weak positive (Vsh > Vsv) and negative (Vsv > Vsh) radial anisotropy in the crust. We observe negative radial anisotropy in the upper crust that is associated mainly with the location of a previously reported mantle plume. The anisotropy could be attributed to the vertical alignment of fossil microcracks or metamorphic foliations due to the upwelling of plume material. A strong positive radial anisotropy is centered at the location of an inferred boundary between the Congo Craton and the Oubanguides Belt that might be related to the preferred orientation of crustal anisotropic minerals associated with shearing in this fault zone. The middle crust is characterized by a widespread negative radial anisotropy that is likely caused by the flow-induced alignment of anisotropic minerals that crystallized during magma intrusion. The magnitude of the radial anisotropy varies systematically from predominantly negative in the middle crust to positive in the lower crust. The imaged patterns of the isotropic velocity and radial anisotropy are consistent with previous studies and agree with regional tectonics.
Strong Exchange Anisotropy in Heavy Atom Radical Ferromagnets
Winter, Stephen
2012-02-01
The discovery twenty years ago of ferromagnetic ordering in ``light atom'' p-block (N, O based) radicals appeared to provide a major conceptual advance, suggesting the possibility of a new era in non-metal molecular magnetism. However, the weak through-space magnetic exchange interactions present in these early radical-based ferromagnets afforded very low Curie temperatures TC (JACS 130, 8414-8425 (2008), JACS 133, 8126-8129 (2011).
Kudo, Kazue; Suzuki, Masahiko; Kojima, Kazuki; Yasue, Tsuneo; Akutsu, Noriko; Diño, Wilson Agerico; Kasai, Hideaki; Bauer, Ernst; Koshikawa, Takanori
2013-10-02
Magnetic domains in ultrathin films form domain patterns, which strongly depend on the magnetic anisotropy. The magnetic anisotropy in Co/Ni multilayers changes with the number of layers. We provide a model to simulate the experimentally observed domain patterns. The model assumes a layer-dependent magnetic anisotropy. With the anisotropy parameter estimated from experimental data, we reproduce the magnetic domain patterns.
DEFF Research Database (Denmark)
Winther, G.
1996-01-01
stress Variation in the rolling plane, which may be as high as 20%, are presented. The traditional Taylor model is applied to the data to account for the effect of texture. However, texture effects alone are not enough to explain all of the observed anisotropy. New models which take the combined effects...... of texture and deformation microstructure into account are presented. The models are based on the Taylor and Sachs models but modified with an anisotropic critical shear stress to account for the effect of the microstructure. The agreement between experimental data and model predictions is definitely better...
Iacocca, Ezio; Dumas, Randy K; Bookman, Lake; Mohseni, Majid; Chung, Sunjae; Hoefer, Mark A; Akerman, Johan
2014-01-31
Magnetic dissipative droplets are localized, strongly nonlinear dynamical modes excited in nanocontact spin valves with perpendicular magnetic anisotropy. These modes find potential application in nanoscale structures for magnetic storage and computation, but dissipative droplet studies have so far been limited to extended thin films. Here, numerical and asymptotic analyses are used to demonstrate the existence and properties of novel solitons in confined structures. As a nanowire's width is decreased with a nanocontact of fixed size at its center, the observed modes undergo transitions from a fully localized two-dimensional droplet into a two-dimensional droplet edge mode and then a pulsating one-dimensional droplet. These solitons are interpreted as dissipative versions of classical, conservative solitons, allowing for an analytical description of the modes and the mechanisms of bifurcation. The presented results open up new possibilities for the study of low-dimensional solitons and droplet applications in nanostructures.
Magnetic anisotropy in nanostructures
Eisenbach, M
2001-01-01
method for solving the LDA Kohn-Sham equation. This extended code allows us to perform fully relativistic calculations to enable us to investigate the spin orbit coupling effects leading to anisotropies and potentially non collinear ordering of magnetic moments in these systems of magnetic inclusions in copper. With this approach we find that depending on the orientation of the atoms along the 100 or 110 direction in copper the ground state orientation of the magnetic moments in the chain is either perpendicular or parallel to the chain direction, when the magnetic dipolar interaction energy is added to the final ab initio result. In this thesis we investigate the effect of magnetic anisotropies in nanostructured materials. The main emphasis in our work presented here is on systems that have an underlying one dimensional structure, like nanowires or atomic chains. In a simple classical one dimensional model we show the rich ground state structure of magnetic orientations one might expect to find in such syste...
CPO-induced seismic anisotropy in UHP eclogites
Institute of Scientific and Technical Information of China (English)
2008-01-01
Ultrahigh-pressure (UHP) eclogites often show strong plastic deformation and anisotropy of seismic properties. We report in this paper the seismic velocity and anisotropy of eclogite calculated from the crystallographic preferred orientations (CPOs) of constituent minerals (garnet, omphacite, quartz and rutile) and single crystal elastic properties. We also compared the calculated results with the measured results in similar eclogites. Our results suggest that (1) Except that garnet is a seismically quasi-isotropic mineral, omphacite, quartz, coesite and rutile all have strong seismic anisotropies (AVp = 23.0%―40.9%, Max. AVs = 18.5%―47.1%). They are the major sources for anisotropy in eclogite. The average seismic velocities are fast in garnet and rutile, moderate in omphacite and coesite, and slow in quartz. (2) The deformed eclogites have the maximum Vp (8.33―8.75 km/s) approximately parallel to foliation and lineation, the minimum Vp (8.25―8.62 km/s) approximately normal to foliation and lineation and the Vp anisotropies of 1.0―1.7%. Their Vs are 4.93―4.97 km/s. The corresponding maximum anisotropies (0.73%―1.78%) of Vs are at 45° to both foliation and lineation and the minimum anisotropies at positions normal to lineation on the foliation plane. The Vs1 polarization planes are approximately parallel to foliation. The mean Vp and Vs of eclogite under UHP peak metamorphism conditions (P = 3―5 GPa, T = 900―1100℃) are estimated to be 3.4%―7.2% and 6.3%―12.1% higher than those at ambient pressure and temperature conditions, respectively. (3) Omphacite component dominates the anisotropy of eclogite while garnet component reduces the anisotropy and increases the seismic velocities. Quartz component has a small effect on the anisotropy but reduces the seismic velocities of eclogite. The effect of rutile component is negligible on seismic properties of eclogite due to its trivial volume fraction. (4) The increase of volume fraction of omphacite
Limits on the ions temperature anisotropy in turbulent intracluster medium
Santo-Lima, R; Pino, E M de Gouveia Dal; Lazarian, A
2016-01-01
Turbulence in the weakly collisional intracluster medium of galaxies (ICM) is able to generate strong thermal velocity anisotropies in the ions (with respect to the local magnetic field direction), if the magnetic moment of the particles is conserved in the absence of Coulomb collisions. In this scenario, the anisotropic MHD turbulence shows a very different statistical behaviour from the isotropic (standard) one and is unable to amplify seed magnetic fields, in disagreement with previous cosmological MHD simulations which are able to explain the observed magnetic fields in the ICM. On the other hand, temperature anisotropy can also drive kinetic instabilities which grow faster near the ions kinetic scales. Observations from the solar wind suggest that these micro- instabilities scatter the ions, thus relaxing the anisotropy. This work aims to compare this relaxation rate with the growth rate of the anisotropies driven by the turbulence. We employ quasilinear theory to estimate the scattering rate provided by...
Tuning Exchange Anisotropy of Exchange-Biased System
Institute of Scientific and Technical Information of China (English)
XU Yan; HU Jing-Guo; R.L.Stamps
2008-01-01
Exchange anisotropy in FM/AFM bilayers has given a lot of static magnetization properties such as enhanced coercivity and magnetization loop shifts.These phenomena are primarily from the effective anisotropies intro-duced into a ferromagnet by exchange coupling with a strongly anisotropic antiferromagnet.These effective anisotropies can also be used to explain the dynamic consequences of exchange-biased bilayers.In this article,the dynamic con-sequences such as exchange-induced susceptibility,exchange-induced permeability,and the corresponding domain wall characteristics in the exchange-biased structures of ferromagnet/antiferromagnetl/antiferromagnet2 are studied.The results show that the second antiferromagnetic layer can largely affect the dynamic consequences of exchange-biased bilayers.Especially in the ease of critical temperature,the effects become more obvious.Practically,the exchange anisotropy of biased bilayer system can be tuned by exchange coupling with the second antiferromagnetic layer.
CoTaZr/Pd multilayer with perpendicular magnetic anisotropy
Directory of Open Access Journals (Sweden)
Yong Chang Lau
2013-08-01
Full Text Available We report a novel perpendicularly magnetized thin film [Co91.5Ta4.5Zr4/Pd]5 multilayer, which exhibits strong perpendicular magnetic anisotropy when grown on 5 nm of Pd and Ru seed layers. The Pd-seeded multilayer annealed at 300 °C shows an effective uniaxial anisotropy constant, Keff = 1.1 MJ m−3, with an anisotropy field as high as 1.6 T. The perpendicular anisotropy is sustained on annealing at 400 °C for 1 h. X-ray diffraction on multilayers with 30 repeats suggests that the use of amorphous CoTaZr reduces the stress of the stack, compared to [Co/Pd] multilayer.
Seasonal anisotropy in handedness.
Jones, Gregory V; Martin, Maryanne
2008-01-01
The preference for using either the left or the right hand has been linked to important human characteristics such as language lateralisation within the cerebral hemispheres, and evidence has been reported that the proportions of different types of handedness may be influenced by factors such as levels of maternal hormones and anxiety. Under such influences, it is possible in principle that distributions of handedness provide evidence of seasonal anisotropy, that is, variation in the direction of handedness for births in different parts of the year. The results of a number of studies are compared here, and shown to provide evidence of a significant tendency for the incidence of left-handed people to be higher among those born in the spring and ensuing months (March-July in the northern hemisphere) than among those born in the remainder of the year, at least among the male population.
Transition from weak to strong cascade in MHD turbulence.
Verdini, Andrea; Grappin, Roland
2012-07-13
The transition from weak to strong turbulence when passing from large to small scales in magnetohydrodynamic (MHD) turbulence with guide field is a cornerstone of anisotropic turbulence theory. We present the first check of this transition, using the Shell-RMHD, which combines a shell model of perpendicular nonlinear coupling and linear propagation along the guide field. This model allows us to reach Reynolds numbers around 10(6). We obtain surprisingly good agreement with the theoretical predictions, with a reduced perpendicular energy spectrum scaling as k(⊥)(-2) at large scales and as k(⊥)(-5/3) at small scales, where critical balance between nonlinear and propagation time is reached. However, even in the strong regime, a high level of excitation is found in the weak coupling region of Fourier space, which is due to the rich frequency spectrum of large eddies. A corollary is that the reduced parallel spectral slope is not a definite test of the spectral anisotropy, contrary to standard belief.
CMB Anisotropy due to Cosmic Strings in an Accelerated Expanding Universe
Rokni, S Y; Bordbar, M R
2013-01-01
We want to find the cosmological constant influence on cosmic microwave background (CMB) anisotropy due to cosmic strings. Considering the space-time metric of a cosmic string under the effect of a positive cosmological constant, the CMB anisotropy is studied. The result shows that a positive cosmological constant (i.e. the presence of cosmic strings in an accelerated expanding universe) weakens the anisotropy so that more strong resolution is needed to detect the corresponding influences on the CMB power spectrum.
Morimoto, Takahiro; Zhong, Shudan; Orenstein, Joseph; Moore, Joel E.
2016-12-01
We study nonlinear magneto-optical responses of metals by a semiclassical Boltzmann equation approach. We derive general formulas for linear and second-order nonlinear optical effects in the presence of magnetic fields that include both the Berry curvature and the orbital magnetic moment. Applied to Weyl fermions, the semiclassical approach (i) captures the directional anisotropy of linear conductivity under a magnetic field as a consequence of an anisotropic B2 contribution, which may explain the low-field regime of recent experiments; and (ii) predicts strong second harmonic generation proportional to B that is enhanced as the Fermi energy approaches the Weyl point, leading to large nonlinear Kerr rotation. Moreover, we show that the semiclassical formula for the circular photogalvanic effect arising from the Berry curvature dipole is reproduced by a full quantum calculation using a Floquet approach.
Reichardt, C L; Zahn, O; Aird, K A; Benson, B A; Bleem, L E; Carlstrom, J E; Chang, C L; Cho, H M; Crawford, T M; Crites, A T; de Haan, T; Dobbs, M A; Dudley, J; George, E M; Halverson, N W; Holder, G P; Holzapfel, W L; Hoover, S; Hou, Z; Hrubes, J D; Joy, M; Keisler, R; Knox, L; Lee, A T; Leitch, E M; Lueker, M; Luong-Van, D; McMahon, J J; Mehl, J; Meyer, S S; Millea, M; Mohr, J J; Montroy, T E; Natoli, T; Padin, S; Plagge, T; Pryke, C; Ruhl, J E; Schaffer, K K; Shirokoff, E; Spieler, H G; Staniszewski, Z; Stark, A A; Story, K; van Engelen, A; Vanderlinde, K; Vieira, J D; Williamson, R
2011-01-01
We present the first three-frequency South Pole Telescope (SPT) cosmic microwave background (CMB) power spectra. The band powers presented here cover angular scales 2000 < ell < 9400 in frequency bands centered at 95, 150, and 220 GHz. At these frequencies and angular scales, a combination of the primary CMB anisotropy, thermal and kinetic Sunyaev-Zel'dovich (SZ) effects, radio galaxies, and cosmic infrared background (CIB) contributes to the signal. We combine Planck and SPT data at 220 GHz to constrain the amplitude and shape of the CIB power spectrum and find strong evidence for non-linear clustering. We explore the SZ results using a variety of cosmological models for the CMB and CIB anisotropies and find them to be robust with one exception: allowing for spatial correlations between the thermal SZ effect and CIB significantly degrades the SZ constraints. Neglecting this potential correlation, we find the thermal SZ power at 150 GHz and ell = 3000 to be 3.65 +/- 0.69 muK^2, and set an upper limit on...
Friction anisotropy in boronated graphite
Energy Technology Data Exchange (ETDEWEB)
Kumar, N., E-mail: niranjan@igcar.gov.in [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Radhika, R. [Crystal Growth Centre, Anna University, Chennai (India); Kozakov, A.T. [Research Institute of Physics, Southern Federal University, Rostov-on-Don (Russian Federation); Pandian, R. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Chakravarty, S. [UGC-DAE CSR, Kalpakkam (India); Ravindran, T.R.; Dash, S.; Tyagi, A.K. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India)
2015-01-01
Graphical abstract: - Highlights: • Friction anisotropy in boronated graphite is observed in macroscopic sliding condition. • Low friction coefficient is observed in basal plane and becomes high in prismatic direction. • 3D phase of boronated graphite transformed into 2D structure after friction test. • Chemical activity is high in prismatic plane forming strong bonds between the sliding interfaces. - Abstract: Anisotropic friction behavior in macroscopic scale was observed in boronated graphite. Depending upon sliding speed and normal loads, this value was found to be in the range 0.1–0.35 in the direction of basal plane and becomes high 0.2–0.8 in prismatic face. Grazing-incidence X-ray diffraction analysis shows prominent reflection of (0 0 2) plane at basal and prismatic directions of boronated graphite. However, in both the wear tracks (1 1 0) plane become prominent and this transformation is induced by frictional energy. The structural transformation in wear tracks is supported by micro-Raman analysis which revealed that 3D phase of boronated graphite converted into a disordered 2D lattice structure. Thus, the structural aspect of disorder is similar in both the wear tracks and graphite transfer layers. Therefore, the crystallographic aspect is not adequate to explain anisotropic friction behavior. Results of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy shows weak signature of oxygen complexes and functional groups in wear track of basal plane while these species dominate in prismatic direction. Abundance of these functional groups in prismatic plane indicates availability of chemically active sites tends to forming strong bonds between the sliding interfaces which eventually increases friction coefficient.
Gell-Mann, Murray; Gell-Mann, Murray; Hartle, James B
1997-01-01
We introduce a condition for the strong decoherence of a set of alternative histories of a closed quantum-mechanical system such as the universe. The condition applies, for a pure initial state, to sets of homogeneous histories that are chains of projections, generally branch-dependent. Strong decoherence implies the consistency of probability sum rules but not every set of consistent or even medium decoherent histories is strongly decoherent. Two conditions characterize a strongly decoherent set of histories: (1) At any time the operators that effectively commute with generalized records of history up to that moment provide the pool from which --- with suitable adjustment for elapsed time --- the chains of projections extending history to the future may be drawn. (2) Under the adjustment process, generalized record operators acting on the initial state of the universe are approximately unchanged. This expresses the permanence of generalized records. The strong decoherence conditions (1) and (2) guarantee wha...
Electromagnetic Instabilities Excited by Electron Temperature Anisotropy
Institute of Scientific and Technical Information of China (English)
陆全明; 王连启; 周艳; 王水
2004-01-01
One-dimensional particle-in-cell simulations are performed to investigate the nonlinear evolution of electromagnetic instabilities excited by the electron temperature anisotropy in homogeneous plasmas with different parameters. The results show that the electron temperature anisotropy can excite the two right-hand electromagnetic instabilities, one has the frequency higher than Ωe, the other is the whistler instability with larger amplitude,and its frequency is below Ωe. Their dispersion relations are consistent with the prediction from the cold plasma theory. In the initial growth stage (prediction from linear theory), the frequency of the dominant mode (the mode whose amplitude is large enough) of the whistler wave almost does not change, but in the saturation stage the situation is different. In the case that the ratio of electron plasma frequency to cyclotron frequency is larger than 1, the frequency of the dominant mode of the whistler wave drifts from high to low continuously. However, for the case of the ratio smaller than 1, besides the original dominant mode of the whistler wave whose frequency is about 2.6ωe, another dominant mode whose frequency is about 1.55ωe also begins to be excited at definite time,and its amplitude increases with time until it exceeds the original dominant mode.
A fully covariant description of CMB anisotropies
Dunsby, P K S
1997-01-01
Starting from the exact non-linear description of matter and radiation, a fully covariant and gauge-invariant formula for the observed temperature anisotropy of the cosmic microwave background (CBR) radiation, expressed in terms of the electric ($E_{ab}$) and magnetic ($H_{ab}$) parts of the Weyl tensor, is obtained by integrating photon geodesics from last scattering to the point of observation today. This improves and extends earlier work by Russ et al where a similar formula was obtained by taking first order variations of the redshift. In the case of scalar (density) perturbations, $E_{ab}$ is related to the harmonic components of the gravitational potential $\\Phi_k$ and the usual dominant Sachs-Wolfe contribution $\\delta T_R/\\bar{T}_R\\sim\\Phi_k$ to the temperature anisotropy is recovered, together with contributions due to the time variation of the potential (Rees-Sciama effect), entropy and velocity perturbations at last scattering and a pressure suppression term important in low density universes. We a...
Texture-induced microwave background anisotropies
Energy Technology Data Exchange (ETDEWEB)
Borrill, J.; Copeland, E.J.; Liddle, A.R.; Stebbins, A.; Veeraraghavan, S. (School of Mathematical and Physical Sciences, University of Sussex, Falmer, Brighton BN1 9QH (United Kingdom) Blackett Laboratory, Imperial College of Science and Technology, Prince Consort Road, London SW7 2BZ (United Kingdom) NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laoratory, Batavia, Illinois 60510 (United States) NASA Goddard Space Flight Center, Code 685, Greenbelt, Maryland 20771 (United States) Steward Observatory, University of Arizona, Tucson, Arizona 85721 (United States))
1994-08-15
We use numerical simulations to calculate the cosmic microwave background anisotropy induced by the evolution of a global texture field, with special emphasis on individual textures. Both spherically symmetric and general configurations are analyzed, and in the latter case we consider field configurations which exhibit unwinding events and also ones which do not. We compare the results given by evolving the field numerically under both the expanded core (XCORE) and nonlinear [sigma] model (NLSM) approximations with the analytic predictions of the NLSM exact solution for a spherically symmetric self-similar (SSSS) unwinding. We find that the random unwinding configuration spots' typical peak height is 60--75 % and angular size typically only 10% of those of the SSSS unwinding, and that random configurations without an unwinding event nonetheless may generate indistinguishable hot and cold spots. A brief comparison is made with other work.
Rational approach to anisotropy of sand
Wu, Wei
1998-11-01
The paper presents a constitutive model for the three-dimensional deformation-strength behaviour of inherently anisotropic sand. Based on non-linear tensorial functions, the model is developed without recourse to the concepts in plasticity theory such as yield surface and plastic potential. Benefited from the fact that no decomposition of strain into elastic and plastic parts is assumed, a unified treatment of anisotropic behaviour of deformation and strength is achieved. Anisotropy is characterized by a vector normal to the bedding plane. The extension of the constitutive model is furnished by incorporating the vector under consideration of the principle of objectivity and the condition of material symmetry. Distinct features of the model are its elegant formulation and its simple structure involving few material parameters. Model performance and comparison with experiments show that the model is capable of capturing the salient behaviour of anisotropic sand.
CMB Anisotropies from a Gradient Mode
Mirbabayi, Mehrdad
2014-01-01
A pure gradient mode must have no observable dynamical effect at linear level. We confirm this by showing that its contribution to the dipolar power asymmetry of CMB anisotropies vanishes, if Maldacena's consistency condition is satisfied. To this end, the existing second order Sachs-Wolfe formula in the squeezed limit is extended to include a gradient in the long mode and to account for the change in the location of the last scattering surface induced by this mode. At second order, a gradient mode generated in Single-field inflation is shown to induce a quadrupole moment. For instance in a matter-dominated model it is equal to 5/18 times the square of the linear gradient part. This quadrupole can be cancelled by superposing a quadratic perturbation. The result is shown to be a non-linear extension of Weinberg's adiabatic modes: a long-wavelength physical mode which looks locally like a coordinate transformation.
Institute of Scientific and Technical Information of China (English)
何其伟; 俞翔; 毛为民
2016-01-01
Cascades of subharmonic waves and their stability for a high-dimensional strongly nonlinear vibration isolation system were studied by combining the harmonic balance method and the predictor-corrector method.The amplitude-frequency curve of every subharmonic wave was plotted.Two routes of bifurcation were analyzed and the boundaries of the period-doubling bifurcations were obtained through the stability analysis,and then the parametric regions of chaos were estimated.The results agreed well with those obtained with numerical simulations.%从次谐波级联角度，利用谐波平衡法与跟踪延拓算法得到了高维强非线性隔振系统各级次谐波的幅频特性曲线，分析了次谐波的稳定性，研究了两条分岔道路，得到了典型的倍周期分岔值，以此估计了混沌参数区域，与数值计算结果吻合较好。
Colossal anisotropy of the magnetic properties of doped lithium nitrodometalates
Energy Technology Data Exchange (ETDEWEB)
Antropov, Vladimir P [Ames Laboratory; Antonov, Victor N [Ames Laboratory
2014-09-01
We present a first-principles investigation of the electronic structure and physical properties of doped lithium nitridometalates Li_{2}(Li_{1-x}M_{x})N (LiMN) with M = Cr, Mn, Fe, Co, and Ni. The diverse properties include the equilibrium magnetic moments, magneto-crystalline anisotropy, magneto-optical Kerr spectra, and x-ray magnetic circular dichroism. We explain the colossal magnetic anisotropy in LiFeN by its unique electronic structure which ultimately leads to a series of unusual physical properties. The most unique property is a complete suppression of relativistic effects and freezing of orbital moments for in-plane orientation of the magnetization. This leads to the colossal spatial anisotropy of many magnetic properties including energy, Kerr, and dichroism effects. LiFeN is identified as an ultimate single-ion anisotropy system where a nearly insulating state can be produced by a spin orbital coupling alone. A very nontrivial strongly fluctuating and sign changing character of the magnetic anisotropy with electronic 3d-atomic doping is predicted theoretically. A large and highly anisotropic Kerr effect due to the interband transitions between atomic-like Fe 3d bands is found for LiFeN. A giant anisotropy of the x-ray magnetic circular dichroism for the Fe K spectrum and a very weak one for the Fe L_{2,3} spectra in LiFeN are also predicted.
Limits on the ions temperature anisotropy in turbulent intracluster medium
Energy Technology Data Exchange (ETDEWEB)
Santos-Lima, R. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Potsdam Univ. (Germany). Inst. fuer Physik und Astronomie; Univ. de Sao Paulo (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas; Yan, H. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Potsdam Univ. (Germany). Inst. fuer Physik und Astronomie; Gouveia Dal Pino, E.M. de [Univ. de Sao Paulo (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas; Lazarian, A. [Wisconsin Univ., Madison, WI (United States). Dept. of Astronomy
2016-05-15
Turbulence in the weakly collisional intracluster medium of galaxies (ICM) is able to generate strong thermal velocity anisotropies in the ions (with respect to the local magnetic field direction), if the magnetic moment of the particles is conserved in the absence of Coulomb collisions. In this scenario, the anisotropic pressure magnetohydrodynamic (AMHD) turbulence shows a very different statistical behaviour from the standard MHD one and is unable to amplify seed magnetic fields, in disagreement with previous cosmological MHD simulations which are successful to explain the observed magnetic fields in the ICM. On the other hand, temperature anisotropies can also drive plasma instabilities which can relax the anisotropy. This work aims to compare the relaxation rate with the growth rate of the anisotropies driven by the turbulence. We employ quasilinear theory to estimate the ions scattering rate due to the parallel firehose, mirror, and ion-cyclotron instabilities, for a set of plasma parameters resulting from AMHD simulations of the turbulent ICM. We show that the ICM turbulence can sustain only anisotropy levels very close to the instabilities thresholds. We argue that the AMHD model which bounds the anisotropies at the marginal stability levels can describe the Alfvenic turbulence cascade in the ICM.
Dynamics of low anisotropy morphologies in directional solidification.
Utter, B; Bodenschatz, E
2002-11-01
We report experimental results on quasi-two-dimensional diffusion limited growth in directionally solidified succinonitrile with small amounts of poly(ethylene oxide), acetone, or camphor as a solute. Seaweed growth, or dense branching morphology, is selected by growing grains close to the [111] plane, where the in-plane surface tension is nearly isotropic. The observed growth morphologies are very sensitive to small anisotropies in surface tension caused by misorientations from the [111] plane. Different seaweed morphologies are found, including the degenerate, the stabilized, and the strongly tilted seaweeds. The degenerate seaweeds show a limited fractal scaling range and, with increased undercooling, suggests a transition from "fractal" to "compact" seaweed. Strongly tilted seaweeds demonstrate a significant twofold anisotropy. In addition, seaweed-dendrite transitions are observed in low anisotropy growth.
Adsorbate Azimuthal Orientation from Reflectance Anisotropy Spectroscopy
Frederick, B. G.; Power, J. R.; Cole, R. J.; Perry, C. C.; Chen, Q.; Haq, S.; Bertrams, Th.; Richardson, N. V.; Weightman, P.
1998-05-01
We have determined the azimuthal orientation of an adsorbate on a metal surface from an intramolecular-transition-derived feature in reflectance anisotropy spectroscopy (RAS). Adsorption of 9-anthracene carboxylic acid onto p\\(2×1\\)O/Cu110 led to an ordered structure with a strong (2%), derivativelike feature at 4.5 eV. Fresnel theory predicts the measured intensity, functional behavior, and sense of the RAS signal for the molecule aligned along [110]. IR measurements confirm that the molecular plane is perpendicular to the surface and STM measurements support the azimuthal orientation. We reassign the sense of the clean Cu(110) surface RA spectrum.
Anisotropies in the HI gas distribution toward 3C 196
Kalberla, P. M. W.; Kerp, J.
2016-10-01
Context. The local Galactic Hi gas was found to contain cold neutral medium (CNM) filaments that are aligned with polarized dust emission. These filaments appear to be dominated by the magnetic field and in this case turbulence is expected to show distinct anisotropies. Aims: We use the Galactic Effelsberg-Bonn Hi Survey (EBHIS) to derive 2D turbulence spectra for the Hi distribution in direction to 3C 196 and two more comparison fields. Methods: Prior to Fourier transform we apply a rotational symmetric 50% Tukey window to apodize the data. We derive average as well as position angle dependent power spectra. Anisotropies in the power distribution are defined as the ratio of the spectral power in orthogonal directions. Results: We find strong anisotropies. For a narrow range in position angle, in direction perpendicular to the filaments and the magnetic field, the spectral power is on average more than an order of magnitude larger than parallel. In the most extreme case the anisotropy reaches locally a factor of 130. Anisotropies increase on average with spatial frequency as predicted by Goldreich & Sridhar (1995, ApJ, 438, 763), at the same time the Kolmogorov spectral index remains almost unchanged. The strongest anisotropies are observable for a narrow range in velocity and decay with a power law index close to -8/3, almost identical to the average isotropic spectral index of -2.9 <γ< -2.6. Conclusions: Hi filaments, associated with linear polarization structures in LOFAR observations in direction to 3C 196, show turbulence spectra with marked anisotropies. Decaying anisotropies appear to indicate that we witness an ongoing shock passing the Hi and affecting the observed Faraday depth.
Ferromagnetic resonance of nanocrystal chains with competitive and cooperative anisotropy
Koulialias, D.
2015-12-01
The formation of cellular magnetic dipoles by chain assemblies of nearly equidimensional, stable single domain magnetite nanocrystals aligned along their [111] easy axes is a common property encountered in many magnetotactic bacteria (MTB). The development of such dipoles permits the navigation of MTB along the geomagnetic field towards favourable habitats, a process also referred to as magnetotaxis. An important characteristic is the anisotropy within the chains, which mainly consists of the magnetocrystalline and the shape anisotropy. The two anisotropy contributions can be cooperative or competitive depending on the orientation with respect to the chain axis. The change in the relative orientation between the two anisotropy contributions caused by the Verwey transition TV, can be used to unambigously detect MTB and their fossil remains. Ferromagnetic resonance spectroscopy (FMR) is a well-established method to probe magnetic anisotropy in absolute units. Here, we use X- and Q-band FMR spectroscopy and numerical simulation to analyze the MTB species of Desulfovibrio magneticus RS-1 with elongated magnetosomes aligned along the [100] hard axis. In this special case, the magnetotaxis above TV is strongly affected by the shape anisotropy of the nanocrystals and it is competitive to the magnetocrystalline anisotropy. Below TV, the change of the easy axis [111] to [100] generates a cooperative system, which can be considered as the optimal case for magnetotaxis, i.e., shape and magnetocrystalline anisotropies are nearly parallel to the MTB chain axis. In summary, the nanocrystal assembly in RS-1 provides another step towards a better understanding of the physics behind magnetotaxis.
Size effects in the magnetic anisotropy of embedded cobalt nanoparticles: from shape to surface.
Oyarzún, Simón; Tamion, Alexandre; Tournus, Florent; Dupuis, Véronique; Hillenkamp, Matthias
2015-10-06
Strong size-dependent variations of the magnetic anisotropy of embedded cobalt clusters are evidenced quantitatively by combining magnetic experiments and advanced data treatment. The obtained values are discussed in the frame of two theoretical models that demonstrate the decisive role of the shape in larger nanoparticles and the predominant role of the surface anisotropy in clusters below 3 nm diameter.
Size effects in the magnetic anisotropy of embedded cobalt nanoparticles: from shape to surface
Simón Oyarzún; Alexandre Tamion; Florent Tournus; Véronique Dupuis; Matthias Hillenkamp
2015-01-01
Strong size-dependent variations of the magnetic anisotropy of embedded cobalt clusters are evidenced quantitatively by combining magnetic experiments and advanced data treatment. The obtained values are discussed in the frame of two theoretical models that demonstrate the decisive role of the shape in larger nanoparticles and the predominant role of the surface anisotropy in clusters below 3 nm diameter.
Without the strong force, there could be no life. The carbon in living matter is synthesised in stars via the strong force. Lighter atomic nuclei become bound together in a process called nuclear fusion. A minor change in this interaction would make life impossible. As its name suggests, the strong force is the most powerful of the 4 forces, yet its sphere of influence is limited to within the atomic nucleus. Indeed it is the strong force that holds together the quarks inside the positively charged protons. Without this glue, the quarks would fly apart repulsed by electromagnetism. In fact, it is impossible to separate 2 quarks : so much energy is needed, that a second pair of quarks is produced. Text for the interactive: Can you pull apart the quarks inside a proton?
Influence of Ground State Spin of Projectile-Target on Fission Anisotropies
Institute of Scientific and Technical Information of China (English)
O.N.Ghodsi; A.N.Behkami
2008-01-01
Fission fragment anisotropies have been investigated for various systems produced in heavy-ion reactions at near and sub-barrier energies.In particular,special attention has been paid to the entrance channel dependence of fragment angular anisotropies.The results of our analysis of the fragment angular anisotropies induced by boron,carbon,and oxygen ions on Thorium and Neptunium targets as well as Fluorine ions on Neptunium target indicate strong dependence of fragment anisotropies on the channel spin,in consistence with the predication of the pre-equilibrium model.
Single-ion anisotropy in the gadolinium pyrochlores studied by electron paramagnetic resonance
Glazkov, V. N.; Zhitomirsky, M. E.; Smirnov, A. I.; Krug von Nidda, H.-A.; Loidl, A.; Marin, C.; Sanchez, J.-P.
2005-07-01
The electron paramagnetic resonance is used to measure the single-ion anisotropy of Gd3+ ions in the pyrochlore structure of (Y1-xGdx)2Ti2O7 . A rather strong easy-plane-type anisotropy is found. The anisotropy constant D is comparable to the exchange integral J in the prototype Gd2Ti2O7 , D≃0.75J , and exceeds the dipolar energy scale. Physical implications of an easy-plane anisotropy for a pyrochlore antiferromagnet are considered. We calculate the magnetization curves at T=0 and discuss phase transitions in a magnetic field.
Secondary anisotropies of the CMB
Aghanim, Nabila; Silk, Joseph
2007-01-01
The Cosmic Microwave Background fluctuations provide a powerful probe of the dark ages of the universe through the imprint of the secondary anisotropies associated with the reionisation of the universe and the growth of structure. We review the relation between the secondary anisotropies and and the primary anisotropies that are directly generated by quantum fluctuations in the very early universe. The physics of secondary fluctuations is described, with emphasis on the ionisation history and the evolution of structure. We discuss the different signatures arising from the secondary effects in terms of their induced temperature fluctuations, polarisation and statistics. The secondary anisotropies are being actively pursued at present, and we review the future and current observational status.
Polarization singularity anisotropy: determining monstardom
Dennis, Mark R
2008-01-01
C points, that is isolated points of circular polarization in transverse fields of varying polarization, are classified morphologically into three distinct types, known as lemons, stars and monstars. These morphologies are interpreted here according to two natural parameters associated with the singularity, namely the anisotropy of the C point, and the polarization azimuth on the anisotropy axis. In addition to providing insight into singularity morphology, this observation applies to the densities of the various morphologies in isotropic random polarization speckle fields.
Model of anisotropic nonlinearity in self-defocusing photorefractive media.
Barsi, C; Fleischer, J W
2015-09-21
We develop a phenomenological model of anisotropy in self-defocusing photorefractive crystals. In addition to an independent term due to nonlinear susceptibility, we introduce a nonlinear, non-separable correction to the spectral diffraction operator. The model successfully describes the crossover between photovoltaic and photorefractive responses and the spatially dispersive shock wave behavior of a nonlinearly spreading Gaussian input beam. It should prove useful for characterizing internal charge dynamics in complex materials and for accurate image reconstruction through nonlinear media.
Kono, Mitsuo
2010-01-01
A nonlinearity is one of the most important notions in modern physics. A plasma is rich in nonlinearities and provides a variety of behaviors inherent to instabilities, coherent wave structures and turbulence. The book covers the basic concepts and mathematical methods, necessary to comprehend nonlinear problems widely encountered in contemporary plasmas, but also in other fields of physics and current research on self-organized structures and magnetized plasma turbulence. The analyses make use of strongly nonlinear models solved by analytical techniques backed by extensive simulations and available experiments. The text is written for senior undergraduates, graduate students, lecturers and researchers in laboratory, space and fusion plasmas.
Proton temperature-anisotropy-driven instabilities in weakly collisional plasmas: Hybrid simulations
Hellinger, Petr
2014-01-01
Kinetic instabilities in weakly collisional, high beta plasmas are investigated using two-dimensional hybrid expanding box simulations with Coulomb collisions modeled through the Langevin equation (corresponding to the Fokker-Planck one). The expansion drives a parallel or perpendicular temperature anisotropy (depending on the orientation of the ambient magnetic field). For the chosen parameters the Coulomb collisions are important with respect to the driver but are not strong enough to keep the system stable with respect to instabilities driven by the proton temperature anisotropy. In the case of the parallel temperature anisotropy the dominant oblique fire hose instability efficiently reduces the anisotropy in a quasilinear manner. In the case of the perpendicular temperature anisotropy the dominant mirror instability generates coherent compressive structures which scatter protons and reduce the temperature anisotropy. For both the cases the instabilities generate temporarily enough wave energy so that the ...
Transmutation of skyrmions to half-solitons driven by the nonlinear optical spin Hall effect.
Flayac, H; Solnyshkov, D D; Shelykh, I A; Malpuech, G
2013-01-04
We show that the spin domains, generated in the linear optical spin Hall effect by the analog of spin-orbit interaction for exciton polaritons, are associated with the formation of a Skyrmion lattice. In the nonlinear regime, the spin anisotropy of the polariton-polariton interactions results in a spatial compression of the domains and in a transmutation of the Skyrmions into oblique half-solitons. This phase transition is associated with both the focusing of the spin currents and the emergence of a strongly anisotropic emission pattern.
Palodhi, L; Pegoraro, F; 10.1088/0741-3335/51/12/125006
2010-01-01
The nonlinear evolution of the Weibel instability driven by the anisotropy of the electron distribution function in a collisionless plasma is investigated in a spatially one-dimensional configuration with a Vlasov code in a two-dimensional velocity space. It is found that the electromagnetic fields generated by this instability cause a strong deformation of the electron distribution function in phase space, corresponding to highly filamented magnetic vortices. Eventually, these deformations lead to the generation of short wavelength Langmuir modes that form highly localized electrostatic structures corresponding to jumps of the electrostatic potential.
Origin of azimuthal seismic anisotropy in oceanic plates and mantle
Becker, Thorsten W.; Conrad, Clinton P.; Schaeffer, Andrew J.; Lebedev, Sergei
2014-09-01
Seismic anisotropy is ubiquitous in the Earth's mantle but strongest in its thermo-mechanical boundary layers. Azimuthal anisotropy in the oceanic lithosphere and asthenosphere can be imaged by surface waves and should be particularly straightforward to relate to well-understood plate kinematics and large-scale mantle flow. However, previous studies have come to mixed conclusions as to the depth extent of the applicability of paleo-spreading and mantle flow models of anisotropy, and no simple, globally valid, relationships exist. Here, we show that lattice preferred orientation (LPO) inferred from mantle flow computations produces a plausible global background model for asthenospheric anisotropy underneath oceanic lithosphere. The same is not true for absolute plate motion (APM) models. A ˜200 km thick layer where the flow model LPO matches observations from tomography lies just below the ˜1200 °C isotherm of a half-space cooling model, indicating strong temperature-dependence of the processes that control the development of azimuthal anisotropy. We infer that the depth extent of shear, and hence the thickness of a relatively strong oceanic lithosphere, can be mapped this way. These findings for the background model, and ocean-basin specific deviations from the half-space cooling pattern, are found in all of the three recent and independent tomographic models considered. Further exploration of deviations from the background model may be useful for general studies of oceanic plate formation and dynamics as well as regional-scale tectonic analyses.
Magnetocrystalline anisotropy and the magnetocaloric effect in Fe2P
Caron, L.; Hudl, M.; Höglin, V.; Dung, N.H.; Gomez, C.P.; Sahlberg, M.; Brück, E.; Andersson, Y.; Nordblad, P.
2013-01-01
Magnetic and magnetocaloric properties of high-purity, giant magnetocaloric polycrystalline and single-crystalline Fe2P are investigated. Fe2P displays a moderate magnetic entropy change, which spans over 70 K and the presence of strong magnetization anisotropy proves this system is not fully itiner
Magnetic anisotropy and porosity of Antarctic chondrites
Hamano,Yozo/Yomogida,Kiyoshi
1982-01-01
Magnetic susceptibility anisotropy and porosity were measured in eleven Antarctic meteorites. These meteorites are ordinary chondrites (H and L type) in various metamorphic stages. Large magnetic anisotropy has been observed in most of the chondrites. The foliation type of the anisotropy, inferred from the shape of the susceptibility ellipsoid indicates that a uniaxial compressional type deformation is responsible for the anisotropy. The degree of the anisotropy and the porosity do not correl...
Anisotropy tuning with the Wilson flow
Borsanyi, S; Fodor, Z; Katz, S D; Krieg, S; Kurth, T; Mages, S; Schafer, A; Szabo, K K
2012-01-01
We use the Wilson flow to define the gauge anisotropy at a given physical scale. We demonstrate the use of the anisotropic flow by performing the tuning of the bare gauge anisotropy in the tree-level Symanzik action for several lattice spacings and target anisotropies. We use this method to tune the anisotropy parameters in full QCD, where we also exploit the diminishing effect of a well chosen smearing on the renormalization of the fermion anisotropy.
Tuneable perpendicular magnetic anisotropy in single crystal [Co/Ni](111) superlattices
Energy Technology Data Exchange (ETDEWEB)
Gottwald, M; Girod, S; Andrieu, S; Mangin, S, E-mail: gottwald@lpm.u-nancy.fr [Institut Jean Lamour, CNRS - Nancy Universite, BP 239, F-54506 Vandoeuvre (France)
2010-06-15
This paper is dedicated to the preparation of thin film with a strong perpendicular to the film plane magnetic anisotropy, behaviour of great interest for spintronics. Single-crystalline [Co/Ni] (111) superlattices have been grown by molecular beam epitaxy. The epitaxial growth of Co and Ni was controlled by using reflection high energy diffraction (RHEED), allowing us to get an accurate control of the thicknesses. The superlattices magnetic properties were studied using magnetometry. All of them exhibit strong perpendicular to the plane magnetic anisotropy. The maximum of magneto-crystalline anisotropy is obtained for one cobalt mo nolayer. A simple model which takes into account surface and volume anisotropy explains the evolution of perpendicular anisotropy in these layers.
Magnetic Moment and Anisotropy of Individual Co Atoms on Graphene
Donati, F.; Dubout, Q.; Autès, G.; Patthey, F.; Calleja, F.; Gambardella, P.; Yazyev, O. V.; Brune, H.
2013-12-01
We report on the magnetic properties of single Co atoms on graphene on Pt(111). By means of scanning tunneling microscopy spin-excitation spectroscopy, we infer a magnetic anisotropy of K=-8.1meV with out-of-plane hard axis and a magnetic moment of 2.2μB. Co adsorbs on the sixfold graphene hollow site. Upon hydrogen adsorption, three differently hydrogenated species are identified. Their magnetic properties are very different from those of clean Co. Ab initio calculations support our results and reveal that the large magnetic anisotropy stems from strong ligand field effects due to the interaction between Co and graphene orbitals.
Giant and Tunable Anisotropy of Nanoscale Friction in Graphene
Almeida, Clara M.; Prioli, Rodrigo; Fragneaud, Benjamin; Cançado, Luiz Gustavo; Paupitz, Ricardo; Galvão, Douglas S.; de Cicco, Marcelo; Menezes, Marcos G.; Achete, Carlos A.; Capaz, Rodrigo B.
2016-08-01
The nanoscale friction between an atomic force microscopy tip and graphene is investigated using friction force microscopy (FFM). During the tip movement, friction forces are observed to increase and then saturate in a highly anisotropic manner. As a result, the friction forces in graphene are highly dependent on the scanning direction: under some conditions, the energy dissipated along the armchair direction can be 80% higher than along the zigzag direction. In comparison, for highly-oriented pyrolitic graphite (HOPG), the friction anisotropy between armchair and zigzag directions is only 15%. This giant friction anisotropy in graphene results from anisotropies in the amplitudes of flexural deformations of the graphene sheet driven by the tip movement, not present in HOPG. The effect can be seen as a novel manifestation of the classical phenomenon of Euler buckling at the nanoscale, which provides the non-linear ingredients that amplify friction anisotropy. Simulations based on a novel version of the 2D Tomlinson model (modified to include the effects of flexural deformations), as well as fully atomistic molecular dynamics simulations and first-principles density-functional theory (DFT) calculations, are able to reproduce and explain the experimental observations.
Edge detection by nonlinear dynamics
Energy Technology Data Exchange (ETDEWEB)
Wong, Yiu-fai
1994-07-01
We demonstrate how the formulation of a nonlinear scale-space filter can be used for edge detection and junction analysis. By casting edge-preserving filtering in terms of maximizing information content subject to an average cost function, the computed cost at each pixel location becomes a local measure of edgeness. This computation depends on a single scale parameter and the given image data. Unlike previous approaches which require careful tuning of the filter kernels for various types of edges, our scheme is general enough to be able to handle different edges, such as lines, step-edges, corners and junctions. Anisotropy in the data is handled automatically by the nonlinear dynamics.
Exotic skyrmion crystals in chiral magnets with compass anisotropy
Chen, J. P.; Zhang, Dan-Wei; Liu, J.-M.
2016-07-01
The compass-type anisotropy appears naturally in diverse physical contexts with strong spin-orbit coupling (SOC) such as transition metal oxides and cold atomic gases etc, and it has been receiving substantial attention. Motivated by recent studies and particularly recent experimental observations on helimagnet MnGe, we investigate the critical roles of this compass-type anisotropy in modulating various spin textures of chiral magnets with strong SOC, by Monte Carlo simulations based on a classical Heisenberg spin model with Dzyaloshinsky-Moriya interaction and compass anisotropy. A phase diagram with emergent spin orders in the space of compass anisotropy and out-of-plane magnetic field is presented. In this phase diagram, we propose that a hybrid super-crystal structure consisting of alternating half-skyrmion and half-anti-skyrmion is the possible zero-field ground state of MnGe. The simulated evolution of the spin structure driven by magnetic field is in good accordance with experimental observations on MnGe. Therefore, this Heisenberg spin model successfully captures the main physics responsible for the magnetic structures in MnGe, and the present work may also be instructive to research on the magnetic states in other systems with strong SOC.
Irreversible magnetic processes under biaxial and uniaxial magnetic anisotropies
Directory of Open Access Journals (Sweden)
S. Pokharel
2016-05-01
Full Text Available Irreversible magnetic processes have been investigated in magnetic systems with two different anisotropy symmetries (uniaxial and biaxial through angular measurement of the switching field, the irreversible susceptibility and the magnetic viscosity. These two systems consist of two-dimensional cobalt ferrite hetero-structures epitaxially grown on (100 and (110 MgO substrate. It is found that for uniaxial anisotropy the irreversible characteristics of the magnetization are large and display a strong angular dependence, which exhibits its maximum at the easy axis and drops quickly to vanish at the hard axis. However, for biaxial anisotropy the magnetization irreversible characteristics are considerably reduced and are less sensitive to the field angle.
Institute of Scientific and Technical Information of China (English)
还毅; 方秦; 陈力; 柳锦春
2011-01-01
In order to investigate the dynamic response and the failure mechanism of metro-station structures under strong seismic loading, a two-dimensional (2D) and a three-dimensional (3D) nonlinear finite element models of the Daikai subway station during Kobe earthquake were established based on damaged plasticity model for concrete, extended Drucker-Prager model for soil, soil-underground structure interaction theory and artificial boundary theory. The 3 D nonlinear responses of the Daikai subway station with isolators fixed at the column ends subjected to seismic loading were also analyzed. The results show that: ( 1 ) the finite element models established in this paper can describe the dynamic properties of the reinforced concrete structure and the dynamic interaction of soil-underground structure properly; (2) the 3D numerical results agree well with the in situ observations by comparison of the numerical results of the 2D and 3D models, and the failure mode of the column in the metrostation structure under seismic loading can not be predicted precisely by the 2D analysis; (3) the 3D shock isolator, composed of dish spring and lead rubber beading, has a rather large vertical stiffness and good resistance to lateral deformation, and consequently can markedly reduce the deformation and damage of the column when fixed at the ends of the column.%为了研究地铁车站结构在强震作用下的动力响应及破坏机理,基于混凝土损伤塑性模型、岩土扩展的Drucker-Prager模型、土-结构相互作用以及人工边界等相关理论,利用ABAQUS软件建立了强震作用下地铁车站的动态响应与损伤破坏的二维、三维精细化非线性有限元分析模型,并对柱端设置隔震器的地铁车站结构进行了三维非线性动力分析.分析结果表明:所建立的有限元分析模型能较好地反映强震荷载作用下钢筋混凝土结构的动力特性以及土-地下结构之间相互作用,适用于地下结构抗震分
Giant dielectric anisotropy via homogenization
Mackay, Tom G
2014-01-01
A random mixture of two isotropic dielectric materials, one composed of oriented spheroidal particles of relative permittivity $\\epsilon_a$ and the other composed of oriented spheroidal particles of relative permittivity $\\epsilon_b$, was considered in the long wavelength regime. The permittivity dyadic of the resulting homogenized composite material (HCM) was estimated using the Bruggeman homogenization formalism. The HCM was an orthorhombic biaxial material if the symmetry axes of the two populations of spheroids were mutually perpendicular and a uniaxial material if these two axes were mutually aligned. The degree of anisotropy of the HCM, as gauged by the ratio of the eigenvalues of the HCM's permittivity dyadic, increased as the shape of the constituent particles became more eccentric. The greatest degrees of HCM anisotropy were achieved for the limiting cases wherein the constituent particles were shaped as needles or discs. In these instances explicit formulas for the HCM anisotropy were derived from t...
Inner Core Anisotropy Due to the Magnetic Field--induced Preferred Orientation of Iron.
Karato, S
1993-12-10
Anisotropy of the inner core of the Earth is proposed to result from the lattice preferred orientation of anisotropic iron crystals during their solidification in the presence of a magnetic field. The resultant seismic anisotropy is related to the geometry of the magnetic field in the core. This hypothesis implies that the observed anisotropy (fast velocity along the rotation axis) indicates a strong toroidal field in the core, which supports a strong field model for the geodynamo if the inner core is made of hexagonal close-packed iron.
Directory of Open Access Journals (Sweden)
Zhaoliang Liao
2014-09-01
Full Text Available La2/3Sr1/3MnO3 films with uniaxial magnetic anisotropy were coherently grown on NdGaO3 (110 substrates. The uniaxial anisotropy has strong effect on magnetoresistance (MR. A positive MR was observed when the current is along magnetic easy axis under the current-field perpendicular geometry. In contrast, no positive MR is observed when current is along the magnetic hard axis regardless of the field direction. Our analysis indicates that the anomalous anisotropic MR effect arises from the uniaxial magnetic anisotropy caused stripe domains which contribute to strong anisotropic domain wall resistivity.
On the origin of perpendicular magnetic anisotropy in strained Fe-Co(-X) films
Reichel, L.; Edström, A.; Pohl, D.; Rusz, J.; Eriksson, O.; Schultz, L.; Fähler, S.
2017-02-01
Very high magnetic anisotropies have been theoretically predicted for strained Fe-Co(-X) and indeed several experiments on epitaxial thin films seemed to confirm strain induced anisotropy enhancement. This study presents a critical analysis of the different contributions to perpendicular anisotropy: volume, interface and surface anisotropies. Tracing these contributions, thickness series of single layer films as well as multilayers with Au-Cu buffers/interlayers of different lattice parameters have been prepared. The analysis of their magnetic anisotropy reveals a negligible influence of the lattice parameter of the buffer. Electronic effects, originating from both, the Au-Cu interface and the film surface, outrange the elastic effects. Surface anisotropy, however, exceeds the interface anisotropy by more than a factor of three. A comparison with results from density functional theory suggests, that the experimentally observed strong perpendicular surface anisotropy originates from a deviation from an ideal oxide-free surface. Accordingly, tailored Fe-Co-X/oxide interfaces may open a route towards high anisotropy in rare-earth free materials.
Magnetic anisotropy of ultrafine 316L stainless steel fibers
Shyr, Tien-Wei; Huang, Shih-Ju; Wur, Ching-Shuei
2016-12-01
An as-received 316L stainless steel fiber with a diameter of 20 μm was drawn using a bundle drawing process at room temperature to form ultrafine stainless steel fibers with diameters of 12, 8, and 6 μm. The crystalline phases of the fibers were analyzed using the X-ray diffraction (XRD) profile fitting technique. The grain sizes of γ-austenite and α‧-martensite were reduced to nanoscale sizes after the drawing process. XRD analysis and focused ion beam-scanning electron microscope observations showed that the newly formed α‧-martensitic grains were closely arrayed in the drawing direction. The magnetic property was measured using a superconducting quantum interference device vibrating sample magnetometer. The magnetic anisotropy of the fibers was observed by applying a magnetic field parallel and perpendicular to the fiber axis. The results showed that the microstructure anisotropy including the shape anisotropy, magnetocrystalline anisotropy, and the orientation of the crystalline phases strongly contributed to the magnetic anisotropy.
Performance of ERNE in particle flux anisotropy measurement
Directory of Open Access Journals (Sweden)
E. Riihonen
Full Text Available The HED particle detector of the ERNE experiment to be flown on the SOHO spacecraft is unique compared to the earlier space-born detectors in its high directional resolution (better than 2°, depending on the track inclination. Despite the fixed view cone due to the three-axis stabilization of the spacecraft, the good angular and temporal resolution of the detector provides a new kind of opportunity for monitoring in detail the development of the anisotropies pertaining, for example, to the onset of SEP events, or passage of shock fronts related to gradual events. In order to optimize the measurement parameters, we have made a preflight simulation study of the HED anisotropy measurement capabilities. The purpose was to prove the feasibility of the selected measurement method and find the physical limits for the HED anisotropy detection. The results show HED to be capable of detecting both strong anisotropies related to impulsive events, and smoother anisotropies associated with gradual events.
Phenomenological description of anisotropy effects in some ferromagnetic superconductors
Energy Technology Data Exchange (ETDEWEB)
Shopova, Diana V., E-mail: sho@issp.bas.bg [TCCM Research Group, Institute of Solid State Physics, Bulgarian Academy of Sciences, BG-1784 Sofia (Bulgaria); Todorov, Michail D. [Department of Applied Mathematics and Computer Science, Technical University of Sofia, 1000 Sofia (Bulgaria)
2015-07-03
We study phenomenologically the role of anisotropy in ferromagnetic superconductors UGe{sub 2}, URhGe, and UCoGe for the description of their phase diagrams. We use the Ginzburg–Landau free energy in its uniform form as we will consider only spatially independent solutions. This is an expansion of previously derived results where the effect of Cooper-pair and crystal anisotropies is not taken into account. The three compounds are separately discussed with the special stress on UGe{sub 2}. The main effect comes from the strong uniaxial anisotropy of magnetization while the anisotropy of Cooper pairs and crystal anisotropy only slightly change the phase diagram in the vicinity of Curie temperature. The limitations of this approach are also discussed. - Highlights: • Anisotropic Landau energy for description of ferromagnetic superconductors is proposed. • Meissner phases are described with their existence and stability conditions. • The application of the model to UGe{sub 2} is discussed. • The limitations to apply the model for description of experimental data are explained.
Anisotropies in the HI gas distribution toward 3C196
Kalberla, P M W
2016-01-01
The local Galactic HI gas was found to contain cold neutral medium (CNM) filaments that are aligned with polarized dust emission. These filaments appear to be dominated by the magnetic field and in this case turbulence is expected to show distinct anisotropies. We use the Galactic Effelsberg--Bonn HI Survey (EBHIS) to derive 2D turbulence spectra for the HI distribution in direction to 3C196 and two more comparison fields. Prior to Fourier transform we apply a rotational symmetric 50% Tukey window to apodize the data. We derive average as well as position angle dependent power spectra. Anisotropies in the power distribution are defined as the ratio of the spectral power in orthogonal directions. We find strong anisotropies. For a narrow range in position angle, in direction perpendicular to the filaments and the magnetic field, the spectral power is on average more than an order of magnitude larger than parallel. In the most extreme case the anisotropy reaches locally a factor of 130. Anisotropies increase on...
Tunable nonlinear graphene metasurfaces
Smirnova, Daria A; Kivshar, Yuri S; Khanikaev, Alexander B
2015-01-01
We introduce the concept of nonlinear graphene metasurfaces employing the controllable interaction between a graphene layer and a planar metamaterial. Such hybrid metasurfaces support two types of subradiant resonant modes, asymmetric modes of structured metamaterial elements ("metamolecules") and graphene plasmons exhibiting strong mutual coupling and avoided dispersion crossing. High tunability of graphene plasmons facilitates strong interaction between the subradiant modes, modifying the spectral position and lifetime of the associated Fano resonances. We demonstrate that strong resonant interaction, combined with the subwavelength localization of plasmons, leads to the enhanced nonlinear response and high efficiency of the second-harmonic generation.
Cosmics cosmological initial conditions and microwave anisotropy codes
Bertschinger, E
1995-01-01
COSMICS is a package of fortran programs useful for computing transfer functions and microwave background anisotropy for cosmological models, and for generating gaussian random initial conditions for nonlinear structure formation simulations of such models. Four programs are provided: {\\bf linger\\_con} and {\\bf linger\\_syn} integrate the linearized equations of general relativity, matter, and radiation in conformal Newtonian and synchronous gauge, respectively; {\\bf deltat} integrates the photon transfer functions computed by the linger codes to produce photon anisotropy power spectra; and {\\bf grafic} tabulates normalized matter power spectra and produces constrained or unconstrained samples of the matter density field. Version 1.0 of COSMICS is available at http://arcturus.mit.edu/cosmics/ . The current release gives fortran-77 programs that run on workstations and vectorized supercomputers. Unix makefiles are included that make it simple to build and test the package. A future release will include portable...
Geometric nonlinearity and mechanical anisotropy in strained helical nanoribbons
Chen, Z.
2014-07-01
Fabrication and synthesis of helical nanoribbons have received increasing attention because of the broad applications of helical nanostructures in nano-elecromechanical/micro-electromechanical systems (NEMS/MEMS), sensors, active materials, drug delivery, etc. In this paper, I study the mechanical principles used in designing strained helical nanoribbons, and propose the use of a full three-dimensional finite element method to simulate the coexistence of both left- and right-handed segments in the same strained nanoribbon. This work can both help understand the large deformation behaviours of such nanostructures and assist in the design of helical nanostructures for engineering applications.
DEFF Research Database (Denmark)
Katajainen, Jyrki
2008-01-01
In this project the goal is to develop the safe * family of containers for the CPH STL. The containers to be developed should be safer and more reliable than any of the existing implementations. A special focus should be put on strong exception safety since none of the existing prototypes available...... at the CPH STL can give this guarantee for all operations. In spite of the safety requirements, the strict running-time requirements specified in the C++ standard, and additional requirements specified in the CPH STL design documents, must be fulfilled....
Anisotropy and Heterogeneity Interaction in Shear Zones
Dabrowski, M.; Schmid, D. W.
2009-04-01
Rocks are heterogeneous on many different scales and deformation may introduce a coexistence of heterogeneity and anisotropy in shear zones. A competent inclusion embedded in a laminated matrix is a typical example. Indisputably, the presence of a mechanical heterogeneity leads to a flow perturbation and consequently to a deflection of the lamination in its vicinity. Assuming a passive response of the matrix phase, the pattern formation around rigid objects has been modeled in two and three dimensions using analytical solutions. Yet, the laminas may be mechanically distinct, leading to an effectively anisotropic rheology of the matrix. The feedback of an evolving matrix structure on the inclusion motion cannot be precluded in this case. In our study elliptical inclusions of varying aspect ratios are embedded in a laminated linear viscous host and subject to a large simple shear deformation in finite element numerical simulations. Increasing the viscosity ratio of the weak and strong lamina significantly changes the pattern characteristics in the matrix. The structural evolution around an inclusion proves to have a major impact on the inclusion motion, leading to the stabilization of elongated inclusions at antithetic orientations. We provide a comparison of two different modeling approaches. In the first approach discrete layers are introduced in the matrix and the large strain evolution of individual minute layers is resolved. Next, the matrix is modeled as an anisotropic medium using an evolving director field that locally describes the anisotropy direction. The length scale of layering can be restored in this model using the micropolar medium formulation.
Texture and anisotropy analysis of Qusaiba shales
Kanitpanyacharoen, Waruntorn
2011-02-17
Scanning and transmission electron microscopy, synchrotron X-ray diffraction, microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried Qusaiba shales from the Rub\\'al-Khali basin, Saudi Arabia. Kaolinite, illite-smectite, illite-mica and chlorite show strong preferred orientation with (001) pole figure maxima perpendicular to the bedding plane ranging from 2.4-6.8 multiples of a random distribution (m.r.d.). Quartz, feldspars and pyrite crystals have a random orientation distribution. Elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution, assuming a nonporous material. The average calculated bulk P-wave velocities are 6.2 km/s (maximum) and 5.5 km/s (minimum), resulting in a P-wave anisotropy of 12%. The calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample. In the ultrasonic experiment, which measures the effects of the shale matrix as well as the effects of porosity, velocities are smaller (P-wave maximum 5.3 km/s and minimum 4.1 km/s). The difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample, which have not been taken into account in the matrix averaging. © 2011 European Association of Geoscientists & Engineers.
Flow stress anisotropy in aluminium
DEFF Research Database (Denmark)
Juul Jensen, D.; Hansen, N.
1990-01-01
The plastic anisotropy of cold-rolled high purity aluminum (99.996%) and commercially pure aluminum (99.6%) has been investigated. Sample parameters were the initial grain size and the degree of plastic strain (ϵ < 3.00). Flow stresses (0.2% offset) were measured at room temperature by uniaxial t...
Guo, Zhen; Yang, Yingjie; Chen, Y. John
2016-10-01
We obtain high-resolution Rayleigh and Love wave phase velocity maps from ambient noise tomography using data recorded by NECESSArray in Northeast China. The resulting radial anisotropic model from the joint inversion of Rayleigh and Love wave dispersion curves reveals strong relationship between the crustal radial anisotropy and tectonic provinces, that is, strong positive anisotropy (Vsh > Vsv) beneath the Songliao Basin and weak radial anisotropy beneath the Xinmeng Belt and Changbaishan Region. The Songliao Basin experienced widespread crustal extension during the late Mesozoic. We interpret the lower crustal anisotropy beneath the Songliao Basin as a result of ductile deformation during the rifting stage, which may lead to the alignment of anisotropic minerals and the observed strong radial anisotropy at present. In the northern Songliao Basin, where thick syn-rift and post-rift sediments (≥4 km) are believed to be present, we observe a broader lateral distribution of anisotropy with stronger amplitude compared with the southern basin. We suggest that the broader distribution of crustal radial anisotropy in the northern basin could be the consequence of outward lower crustal flow driven by the sedimentary loading during the post-rift stage, which is also proposed by previous numerical modeling.
Nonlinear Effects in the Cosmic Microwave Background
Maartens, R
2000-01-01
Major advances in the observation and theory of cosmic microwave background anisotropies have opened up a new era in cosmology. This has encouraged the hope that the fundamental parameters of cosmology will be determined to high accuracy in the near future. However, this optimism should not obscure the ongoing need for theoretical developments that go beyond the highly successful but simplified standard model. Such developments include improvements in observational modelling (e.g. foregrounds, non-Gaussian features), extensions and alternatives to the simplest inflationary paradigm (e.g. non-adiabatic effects, defects), and investigation of nonlinear effects. In addition to well known nonlinear effects such as the Rees-Sciama and Ostriker-Vishniac effects, further nonlinear effects have recently been identified. These include a Rees-Sciama-type tensor effect, time-delay effects of scalar and tensor lensing, nonlinear Thomson scattering effects and a nonlinear shear effect. Some of the nonlinear effects and th...
Pressure anisotropy and small spatial scales induced by velocity shear
Del Sarto, D.; Pegoraro, F.; Califano, F.
2016-05-01
By including the full pressure tensor dynamics in a fluid plasma model, we show that a sheared velocity field can provide an effective mechanism that makes the initial isotropic pressure nongyrotropic. This is distinct from the usual gyrotropic anisotropy related to the fluid compressibility and usually accounted for in double-adiabatic models. We determine the time evolution of the pressure agyrotropy and discuss how the propagation of "magnetoelastic perturbations" can affect the pressure tensor anisotropization and its spatial filamentation, which are due to the action of both the magnetic field and the flow strain tensor. We support this analysis with a numerical integration of the nonlinear equations describing the pressure tensor evolution.
CMB Anisotropies at Second-Order II: Analytical Approach
Bartolo, N; Riotto, Antonio; Bartolo, Nicola; Matarrese, Sabino; Riotto, Antonio
2007-01-01
We provide an analytical approach to the second-order Cosmic Microwave Background (CMB) anisotropies generated by the non-linear dynamics taking place at last scattering. We study the acoustic oscillations of the photon-baryon fluid in the tight coupling limit and we extend at second-order the Meszaros effect.We allow for a generic set of initial conditions due to primordial non-Gaussianity and we compute all the additional contributions arising at recombination. Our results are useful to provide the full second-order radiation transfer function at all scales necessary for establishing the level of non-Gaussianity in the CMB.
Superweak asthenosphere in light of upper mantle seismic anisotropy
Becker, Thorsten W.
2017-05-01
Earth's upper mantle includes a ˜200 km thick asthenosphere underneath the plates where viscosity and seismic velocities are reduced compared to the background. This zone of weakness matters for plate dynamics and may be required for the generation of plate tectonics itself. However, recent seismological and electromagnetic studies indicate strong heterogeneity in thinner layers underneath the plates which, if related to more extreme, global viscosity reductions, may require a revision of our understanding of mantle convection. Here, I use dynamically consistent mantle flow modeling and the constraints provided by azimuthal seismic anisotropy as well as plate motions to explore the effect of a range of global and local viscosity reductions. The fit between mantle flow model predictions and observations of seismic anisotropy is highly sensitive to radial and lateral viscosity variations. I show that moderate suboceanic viscosity reductions, to ˜0.01-0.1 times the upper mantle viscosity, are preferred by the fit to anisotropy and global plate motions, depending on layer thickness. Lower viscosities degrade the fit to azimuthal anisotropy. Localized patches of viscosity reduction, or layers of subducted asthenosphere, however, have only limited additional effects on anisotropy or plate velocities. This indicates that it is unlikely that regional observations of subplate anomalies are both continuous and indicative of dramatic viscosity reduction. Locally, such weak patches may exist and would be detectable by regional anisotropy analysis, for example. However, large-scale plate dynamics are most likely governed by broad continent-ocean asthenospheric viscosity contrasts rather than a thin, possibly high melt fraction layer.
Directory of Open Access Journals (Sweden)
Yongxiang eLi
2014-05-01
Full Text Available Post-depositional compaction is an integral part of sedimentary rock formation and thus has been reasonably deemed as a major culprit for the long-recognized inclination-shallowing problem in sedimentary rocks. Although theoretical treatment elegantly envisions magnetic anisotropy (or oblate fabrics to correspond to the degree of compaction and the magnitude of inclination flattening, such correspondence has rarely been seen in nature quantitavely, which leaves the possibility of misidentification and/or over-correction for inclination shallowing using magnetic anisotropy. This is because the extent to which oblate magnetic fabrics are developed strongly enough for inclination to start becoming shallow is not yet known. Here, we present sedimentary paleomagnetic data from two ~6 m long gravity cores GHE24L and GHE27L from the northern slope of the South China Sea to examine the down-core changes in magnetic anisotropy and inclinations, and to explore the possible connection between the two parameters. The results show that oblate fabrics are dominantly developed at depths >~2m and the degree of anisotropy displays an overall gradual increase with depth. Inclination shallowing occurs in the > 5m segment of the relatively distal core GHE27L and the amount of shallowing largely correlates with the degree of anisotropy, suggesting a causal relation between the development of magnetic anisotropy and the degree of inclination shallowing. Examination of down-core changes in inclination and magnetic anisotropy suggests that a threshold anisotropy of PAMS~1.04 and PAAR~1.10 exists for inclination shallowing in the cores. For PAAR10° if particle anisotropy is <1.4. This study provides strong field evidence that complements and substantiates the theoretical model and suggests that the threshold anisotropy can be used as a first-order criterion to identify inclination errors of some sedimentary rocks.
Magnetic anisotropy of lecithin membranes. A new anisotropy susceptometer.
Scholz, F.; Boroske, E; Helfrich, W.
1984-01-01
Cylindrical giant vesicles prepared from egg lecithin and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are oriented in an external magnetic field and observed by phase contrast microscopy. The anisotropic part of the diamagnetic susceptibility of the lecithin membrane is determined from the distribution of angles between the magnetic field and the long cylinder axis due to thermal fluctuations. The anisotropy of DMPC is found to be larger by a factor of 2 than that of egg lecithin. This...
The strong side of weak topological insulators
Kraus, Yaacov; Ringel, Zohar; Stern, Ady
2012-02-01
Three-dimensional topological insulators are classified into ``strong'' (STI) and ``weak'' (WTI) according to the nature of their surface states. While the surface states of the STI are topologically protected, in the WTI they are believed to be very fragile to disorder. In this work we show that the WTI surface states are actually protected from any random perturbation which does not break time-reversal symmetry, and does not close the bulk energy gap. Consequently, the conductivity of metallic surfaces in the clean system will remain finite even in the presence of strong disorder of this type. In the weak disorder limit the surfaces are perfect metals, and strong surface disorder only acts to push them inwards. We find that WTI's differ from STI's primarily in their anisotropy, and that the anisotropy is not a sign of their weakness but rather of their richness.
Effect of induced shape anisotropy on magnetic properties of ferromagnetic cobalt nanocubes.
Srikala, D; Singh, V N; Banerjee, A; Mehta, B R
2010-12-01
We report on the synthesis of ferromagnetic cobalt nanocubes of various sizes using thermal pyrolysis method and the effect of shape anisotropy on the static and dynamic magnetic properties were studied. Shape anisotropy of approximately 10% was introduced in nanocubes by making nanodiscs using a linear chain amine surfactant during synthesis process. It has been observed that, ferromagnetism persisted above room temperature and a sharp drop in magnetic moment at low temperatures in zero-field cooled magnetization may be associated with the spin disorder due to the effective anisotropy present in the system. Dynamic magnetic properties were studied using RF transverse susceptibility measurements at different temperatures and the singularities due to anisotropy fields were probed at low temperatures. Symmetrically located broad peaks are observed in the frozen state at the effective anisotropy fields and the peak structure is strongly affected by shape anisotropy and temperature. Irrespective of size the shape anisotropy gave rise to higher coercive fields and larger transverse susceptibility ratio at all temperatures. The role of shape anisotropy and the size of the particles on the observed magnetic behaviour were discussed.
Orthotropic Laminated Open-cell Frameworks Retaining Strong Auxeticity under Large Uniaxial Loading
Tanaka, Hiro; Suga, Kaito; Iwata, Naoki; Shibutani, Yoji
2017-01-01
Anisotropic materials form inside living tissue and are widely applied in engineered structures, where sophisticated structural and functional design principles are essential to employing these materials. This paper presents a candidate laminated open-cell framework, which is an anisotropic material that shows remarkable mechanical performance. Using additive manufacturing, artificial frameworks are fabricated by lamination of in-plane orthotropic microstructures made of elbowed beam and column members; this fabricated structure features orthogonal anisotropy in three-dimensional space. Uniaxial loading tests reveal strong auxeticity (high negative Poisson’s ratios) in the out-of-plane direction, which is retained reproducibly up to the nonlinear elastic region, and is equal under tensile and compressive loading. Finite element simulations support the observed auxetic behaviors for a unit cell in the periodic framework, which preserve the theoretical elastic properties of an orthogonal solid. These findings open the possibility of conceptual materials design based on geometry.
Where is magnetic anisotropy field pointing to?
Gutowski, Marek W
2013-01-01
The desired result of magnetic anisotropy investigations is the determination of value(s) of various anisotropy constant(s). This is sometimes difficult, especially when the precise knowledge of saturation magnetization is required, as it happens in ferromagnetic resonance (FMR) studies. In such cases we usually resort to `trick' and fit our experimental data to the quantity called \\emph{anisotropy field}, which is strictly proportional to the ratio of the searched anisotropy constant and saturation magnetization. Yet, this quantity is scalar, simply a number, and is therefore of little value for modeling or simulations of the magnetostatic or micromagnetic structures. Here we show how to `translate' the values of magnetic anisotropy constants into the complete vector of magnetic anisotropy field. Our derivation is rigorous and covers the most often encountered cases, from uniaxial to cubic anisotropy.
CMB anisotropies from a gradient mode
Mirbabayi, Mehrdad; Zaldarriaga, Matias
2015-03-01
A linear gradient mode must have no observable dynamical effect on short distance physics. We confirm this by showing that if there was such a gradient mode extending across the whole observable Universe, it would not cause any hemispherical asymmetry in the power of CMB anisotropies, as long as Maldacena's consistency condition is satisfied. To study the effect of the long wavelength mode on short wavelength modes, we generalize the existing second order Sachs-Wolfe formula in the squeezed limit to include a gradient in the long mode and to account for the change in the location of the last scattering surface induced by this mode. Next, we consider effects that are of second order in the long mode. A gradient mode Φ = qṡx generated in Single-field inflation is shown to induce an observable quadrupole moment. For instance, in a matter-dominated model it is equal to Q = 5(qṡx)2/18. This quadrupole can be canceled by superposition of a quadratic perturbation. The result is shown to be a nonlinear extension of Weinberg's adiabatic modes: a long-wavelength physical mode which looks locally like a coordinate transformation.
Deciphering the Dipole Anisotropy of Galactic Cosmic Rays
Ahlers, Markus
2016-01-01
Recent measurements of the dipole anisotropy in the arrival directions of Galactic cosmic rays (CRs) indicate a strong energy dependence of the dipole amplitude and phase in the TeV-PeV range. We argue here that these observations can be well understood within standard diffusion theory as a combined effect of (i) one or more local sources at Galactic longitude 120deg < l < 300deg dominating the CR gradient below 0.1-0.3 PeV, (ii) the presence of a strong ordered magnetic field in our local environment, (iii) the relative motion of the solar system, and (iv) the limited reconstruction capabilities of ground-based observatories. We show that an excellent candidate of the local CR source responsible for the dipole anisotropy at 1-100 TeV is the Vela supernova remnant.
Magnetic anisotropy and quantized spin waves in hematite nanoparticles
DEFF Research Database (Denmark)
Klausen, Stine Nyborg; Lefmann, Kim; Lindgård, Per-Anker
2004-01-01
We report on the observation of high-frequency collective magnetic excitations, (h) over bar omegaapproximate to1.1 meV, in hematite (alpha-Fe2O3) nanoparticles. The neutron scattering experiments include measurements at temperatures in the range 6-300 K and applied fields up to 7.5 T as well...... the temperature dependence of the magnetic anisotropy, which is strongly related to the suppression of the Morin transition in nanoparticles of hematite. Further, the localization of the signal in both energy and momentum transfer brings evidence for finite-size quantization of spin waves in the system....... as polarization analysis. We give an explanation for the field- and temperature dependence of the excitations, which are found to have strongly elliptical out-of-plane precession. The frequency of the excitations gives information on the magnetic anisotropy constants in the system. We have in this way determined...
Anisotropies in the gravitational wave background from preheating.
Bethke, Laura; Figueroa, Daniel G; Rajantie, Arttu
2013-07-05
We investigate the anisotropies in the gravitational wave (GW) background produced at preheating after inflation. Using lattice field theory simulations of a massless preheating model, we show that the GW amplitude depends sensitively on the value of the decay product field χ coupled to the inflaton φ, with the only requisite that χ is light during inflation. We find a strong anisotropy in the amplitude of the GW background on large angular scales, the details of which strongly depend on the reheating dynamics. We expect similar conclusions for a wide class of inflationary models with light scalar fields. If future direct detection GW experiments are capable of detecting the GW produced by preheating, they should also be able to detect this effect. This could eventually provide a powerful way to distinguish between different inflationary and preheating scenarios.
Strongly anisotropic wetting on one-dimensional nanopatterned surfaces.
Xia, Deying; Brueck, S R J
2008-09-01
This communication reports strongly anisotropic wetting behavior on one-dimensional nanopatterned surfaces. Contact angles, degree of anisotropy, and droplet distortion are measured on micro- and nanopatterned surfaces fabricated with interference lithography. Both the degree of anisotropy and the droplet distortion are extremely high as compared with previous reports because of the well-defined nanostructural morphology. The surface is manipulated to tune with the wetting from hydrophobic to hydrophilic while retaining the structural wetting anisotropy with a simple silica nanoparticle overcoat. The wetting mechanisms are discussed. Potential applications in microfluidic devices and evaporation-induced pattern formation are demonstrated.
Magnetocrystalline anisotropy of RCo 5 intermetallics: itinerant-electron contribution
Steinbeck, L.; Richter, M.; Eschrig, H.
2001-05-01
The itinerant-state magnetocrystalline anisotropy energies (MAE) of RCo 5 (R=Y, La, Pr, Nd, Sm, Gd) have been determined by relativistic density-functional calculations in local spin density approximation, with additionally taking into account orbital polarization. The calculated MAEs are found to be strongly affected by changes of the lattice geometry ( c/ a ratio and volume) resulting from (a) uniaxial strain in YCo 5 and (b) the lanthanide contraction along the RCo 5 series.
Investigation of magnetic properties in thick CoFeB alloy films for controllable anisotropy
Energy Technology Data Exchange (ETDEWEB)
Wang, Ke; Huang, Ya; Chen, Ruofei; Xu, Zhan [Huaqiao University, College of Information Science and Engineering, Xiamen City (China)
2016-02-15
CoFeB alloy material has attracted interest for its wide uses in magnetic memory devices and sensors. We investigate magnetic properties of thick Co{sub 40}Fe{sub 40}B{sub 20} films in the thickness range from 10 to 100 nm sandwiched by MgO and Ta layers. Strong in-plane uniaxial magnetic anisotropy is revealed in the as-deposited amorphous films by angular dependent magnetic measurements, and the growth-induced anisotropy is found to strongly depend on the film thickness. A fourfold cubic magnetic anisotropy develops with annealing, as a result of improved crystalline structure in films confirmed by X-ray diffraction measurements. The observed magnetic properties can be explained by the superposition of the uniaxial and additional cubic magnetic anisotropy, tuned by annealing temperature. (orig.)
Investigation of magnetic properties in thick CoFeB alloy films for controllable anisotropy
Wang, Ke; Huang, Ya; Chen, Ruofei; Xu, Zhan
2016-02-01
CoFeB alloy material has attracted interest for its wide uses in magnetic memory devices and sensors. We investigate magnetic properties of thick Co40Fe40B20 films in the thickness range from 10 to 100 nm sandwiched by MgO and Ta layers. Strong in-plane uniaxial magnetic anisotropy is revealed in the as-deposited amorphous films by angular dependent magnetic measurements, and the growth-induced anisotropy is found to strongly depend on the film thickness. A fourfold cubic magnetic anisotropy develops with annealing, as a result of improved crystalline structure in films confirmed by X-ray diffraction measurements. The observed magnetic properties can be explained by the superposition of the uniaxial and additional cubic magnetic anisotropy, tuned by annealing temperature.
Field-dependent perpendicular magnetic anisotropy in CoFeB thin films
Energy Technology Data Exchange (ETDEWEB)
Barsukov, I., E-mail: ibarsuko@uci.edu; Krivorotov, I. N. [Physics and Astronomy, University of California, Irvine, California 92697 (United States); Fu, Yu [INAC/CEA, Grenoble, 17 avenue des Martyrs, Grenoble 38054 (France); Fakultät für Physik and Center for Nanointegration (CeNIDE), Universität Duisburg-Essen, Duisburg 47048 (Germany); Gonçalves, A. M.; Sampaio, L. C. [Physics and Astronomy, University of California, Irvine, California 92697 (United States); Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, Rio de Janeiro 22.290-180, RJ (Brazil); Spasova, M.; Farle, M. [Fakultät für Physik and Center for Nanointegration (CeNIDE), Universität Duisburg-Essen, Duisburg 47048 (Germany); Arias, R. E. [Departamento de Física, FCFM, Universidad de Chile, Casilla 487-3, Santiago (Chile)
2014-10-13
We report ferromagnetic resonance measurements of perpendicular magnetic anisotropy in thin films of Ta/Co{sub 20}Fe{sub 60}B{sub 20}/MgO as a function of the Co{sub 20}Fe{sub 60}B{sub 20} layer thickness. The first and second order anisotropy terms show unexpectedly strong dependence on the external magnetic field applied to the system during the measurements. We propose strong interfacial spin pinning as a possible origin of the field-dependent anisotropy. Our results imply that high-field anisotropy measurements cannot be directly used for quantitative evaluation of zero-field performance parameters of CoFeB-based devices such as spin torque memory.
Bloembergen, Nicolaas
1996-01-01
Nicolaas Bloembergen, recipient of the Nobel Prize for Physics (1981), wrote Nonlinear Optics in 1964, when the field of nonlinear optics was only three years old. The available literature has since grown by at least three orders of magnitude.The vitality of Nonlinear Optics is evident from the still-growing number of scientists and engineers engaged in the study of new nonlinear phenomena and in the development of new nonlinear devices in the field of opto-electronics. This monograph should be helpful in providing a historical introduction and a general background of basic ideas both for expe
Perpendicular magnetic anisotropy in the Heusler alloy Co2TiSi/GaAs(001 hybrid structure
Directory of Open Access Journals (Sweden)
M. T. Dau
2015-05-01
Full Text Available Investigation of the thickness dependence of the magnetic anisotropy in B2-type Co2TiSi films on GaAs(001, shows a pronounced perpendicular magnetic anisotropy at 10 K for thicknesses up to 13.5 nm. We have evidenced that the interfacial anisotropy induced by interface clusters has a strong influence on the perpendicular magnetic anisotropy of this hybrid structure, especially at temperatures lower than the blocking temperature of the clusters (28 K. However, as this influence can be ruled out at higher temperatures, the perpendicular magnetic anisotropy which is found to persist up to room-temperature can be ascribed to the magnetic properties of the Co2TiSi films. For thicknesses larger than 15.0 nm, we observe an alignment of the magnetic easy axis parallel to the sample surface, which is most likely due to the shape anisotropy and the film structure.
Probing strongly coupled anisotropic plasmas from higher curvature gravity
Energy Technology Data Exchange (ETDEWEB)
Jahnke, Viktor; Misobuchi, Anderson Seigo [Universidade de Sao Paulo, Instituto de Fisica, Sao Paulo (Brazil)
2016-06-15
We consider five-dimensional AdS-axion-dilaton gravity with a Gauss-Bonnet term and use a black brane solution displaying spatial anisotropy as the gravity dual of a strongly coupled anisotropic plasma. We compute several observables relevant to the study of the plasma, namely, the drag force, the jet quenching parameter, the quarkonium potential, and the thermal photon production. The effects of higher derivative corrections and of the anisotropy are discussed and compared with previous results. (orig.)
Probing strongly coupled anisotropic plasmas from higher curvature gravity
Misobuchi, Anderson Seigo
2015-01-01
We consider five-dimensional AdS-axion-dilaton gravity with a Gauss-Bonnet term and use a black brane solution displaying spatial anisotropy as the gravity dual of a strongly coupled anisotropic plasma. We compute several observables relevant to the study of the plasma, namely, the drag force, the jet quenching parameter, the quarkonium potential and the thermal photon production. The effects of higher derivative corrections and of the anisotropy are discussed and compared with previous results.
Probing strongly coupled anisotropic plasmas from higher curvature gravity
Jahnke, Viktor; Misobuchi, Anderson Seigo
2016-06-01
We consider five-dimensional AdS-axion-dilaton gravity with a Gauss-Bonnet term and use a black brane solution displaying spatial anisotropy as the gravity dual of a strongly coupled anisotropic plasma. We compute several observables relevant to the study of the plasma, namely, the drag force, the jet quenching parameter, the quarkonium potential, and the thermal photon production. The effects of higher derivative corrections and of the anisotropy are discussed and compared with previous results.
Anisotropy signature in reverse-time migration extended images
Sava, Paul C.
2014-11-04
Reverse-time migration can accurately image complex geologic structures in anisotropic media. Extended images at selected locations in the Earth, i.e., at common-image-point gathers, carry rich information to characterize the angle-dependent illumination and to provide measurements for migration velocity analysis. However, characterizing the anisotropy influence on such extended images is a challenge. Extended common-image-point gathers are cheap to evaluate since they sample the image at sparse locations indicated by the presence of strong reflectors. Such gathers are also sensitive to velocity error that manifests itself through moveout as a function of space and time lags. Furthermore, inaccurate anisotropy leaves a distinctive signature in common-image-point gathers, which can be used to evaluate anisotropy through techniques similar to the ones used in conventional wavefield tomography. It specifically admits a V-shaped residual moveout with the slope of the "V" flanks depending on the anisotropic parameter η regardless of the complexity of the velocity model. It reflects the fourth-order nature of the anisotropy influence on moveout as it manifests itself in this distinct signature in extended images after handling the velocity properly in the imaging process. Synthetic and real data observations support this assertion.
Energy Technology Data Exchange (ETDEWEB)
Geniet, F; Leon, J [Physique Mathematique et Theorique, CNRS-UMR 5825, 34095 Montpellier (France)
2003-05-07
A nonlinear system possessing a natural forbidden band gap can transmit energy of a signal with a frequency in the gap, as recently shown for a nonlinear chain of coupled pendulums (Geniet and Leon 2002 Phys. Rev. Lett. 89 134102). This process of nonlinear supratransmission, occurring at a threshold that is exactly predictable in many cases, is shown to have a simple experimental realization with a mechanical chain of pendulums coupled by a coil spring. It is then analysed in more detail. First we go to different (nonintegrable) systems which do sustain nonlinear supratransmission. Then a Josephson transmission line (a one-dimensional array of short Josephson junctions coupled through superconducting wires) is shown to also sustain nonlinear supratransmission, though being related to a different class of boundary conditions, and despite the presence of damping, finiteness, and discreteness. Finally, the mechanism at the origin of nonlinear supratransmission is found to be a nonlinear instability, and this is briefly discussed here.
Anisotropic Friedmann-Robertson-Walker universe from nonlinear massive gravity
Gumrukcuoglu, A Emir; Mukohyama, Shinji
2012-01-01
In the scope of the nonlinear massive gravity, we study fixed points of evolution equations for a Bianchi type--I universe. We find a new attractor solution with non-vanishing anisotropy, on which the physical metric is isotropic but the Stuckelberg configuration is anisotropic. As a result, at the background level, the solution describes a homogeneous and isotropic universe, while a statistical anisotropy is expected from perturbations, suppressed by smallness of the graviton mass.
Measurement of ﬁssion anisotropy for 16O+181Ta
Indian Academy of Sciences (India)
Bivash R Behera; Subinit Roy; P Basu; M K Sharan; S Jena; M Satpathy; M L Chatterjee; S K Datta
2001-07-01
Anisotropies in ﬁssion fragment angular distributions measured for the system 16O+181Ta over a range of bombarding energies from 83 MeV to 120 MeV have been analysed. It is shown that statistical transition state model (TSM) with pre-scission neutron correction described adequately the measured anisotropy data. Strong friction parameter is found to be necessary to estimate the pre-saddle to pre-scission neutron ratio.
Nonlinearity in nanomechanical cantilevers
DEFF Research Database (Denmark)
Villanueva Torrijo, Luis Guillermo; Karabalin, R. B.; Matheny, M. H.
2013-01-01
Euler-Bernoulli beam theory is widely used to successfully predict the linear dynamics of micro-and nanocantilever beams. However, its capacity to characterize the nonlinear dynamics of these devices has not yet been rigorously assessed, despite its use in nanoelectromechanical systems development....... These findings underscore the delicate balance between inertial and geometric nonlinear effects in the fundamental mode, and strongly motivate further work to develop theories beyond the Euler-Bernoulli approximation. DOI: 10.1103/PhysRevB.87.024304....... In this article, we report the first highly controlled measurements of the nonlinear response of nanomechanical cantilevers using an ultralinear detection system. This is performed for an extensive range of devices to probe the validity of Euler-Bernoulli theory in the nonlinear regime. We find that its...
Directory of Open Access Journals (Sweden)
Ke Xu
2017-05-01
Full Text Available Microstructures of magnetic materials, including defects and crystallographic orientations, are known to strongly influence magnetic domain structures. Measurement techniques such as magnetic force microscopy (MFM thus allow study of correlations between microstructural and magnetic properties. The present work probes effects of anisotropy and artificial defects on the evolution of domain structure with applied field. Single crystal iron thin films on MgO substrates were milled by Focused Ion Beam (FIB to create different magnetically isolated squares and rectangles in [110] crystallographic orientations, having their easy axis 45° from the sample edge. To investigate domain wall response on encountering non-magnetic defects, a 150 nm diameter hole was created in the center of some samples. By simultaneously varying crystal orientation and shape, both magnetocrystalline anisotropy and shape anisotropy, as well as their interaction, could be studied. Shape anisotropy was found to be important primarily for the longer edge of rectangular samples, which exaggerated the FIB edge effects and provided nucleation sites for spike domains in non-easy axis oriented samples. Center holes acted as pinning sites for domain walls until large applied magnetic fields. The present studies are aimed at deepening the understanding of the propagation of different types of domain walls in the presence of defects and different crystal orientations.
Correlations between Thermal and Sonic Anisotropy for Low-Permeable Reservoirs
Popov, Yury; Chekhonin, Evgeny; Popov, Evgeny; Spasennykh, Mikhail; Ovcharenko, Yury; Zhukov, Vladislav; Martemyanov, Andrey
2016-04-01
Rock anisotropy plays an important role in geophysics. Knowledge of thermal anisotropy is necessary for reconstruction of thermal history of a basin and analysis of temperature logging data, while an acoustic anisotropy in sedimentary rocks has a significant impact on seismic processing and reservoir characterization. However, determination of anisotropy for real problems is a complex procedure usually. Common measurements on cores require sampling several plugs in different directions that led to the problem of rock heterogeneity influence. Moreover, full size cores will be destroyed in this case, that makes the approach time-consuming and not reliable often. Determination of anisotropy from sonic logging depends on the quality of the acoustic signal, borehole and mud conditions as well as the direction of the borehole with respect to the anisotropic axes of symmetry. To improve quality of rock anisotropy study we combined the sonic logging data with fast, non-contact non-destructive measurements of principal thermal conductivity tensor components on more than 2000 full-size cores. It provided a comprehensive analysis of variations in thermal and acoustic anisotropy along two wells drilled in low-permeable formations in West Siberia (Russia). Strong correlation between thermal and acoustic anisotropy was established within Bazhen formation (B.fm.). It can be used for prediction of acoustic anisotropy via results of thermal profiling on cores in the intervals, where quantitative analysis of sonic log is impossible (If core is absent, thermal anisotropy can be estimated on cavings and large cuttings using optical scanning method). The work was supported by the Russian Ministry of Education and Science, project No. RFMEFI58114X0008.
Nonlinear optomechanical paddle nanocavities
Kaviani, Hamidreza; Wu, Marcelo; Ghobadi, Roohollah; Barclay, Paul E
2014-01-01
A photonic crystal optomechanical system combining strong nonlinear optomechanical coupling, low effective mass and large optical mode spacing is introduced. This nanoscale "paddle nanocavity" device supports mechanical resonances with effective mass of 300--600 fg which couple nonlinearly to co-localized optical modes with a quadratic optomechanical coupling coefficient $g^{(2)} > 2\\pi\\times400$ MHz/nm$^2$, and a two phonon to single photon optomechanical coupling rate $\\Delta \\omega_0 > 2\\pi\\times 16$ Hz. This coupling relies on strong phonon-photon interactions in a structure whose optical mode spectrum is highly non--degenerate. Simulations indicate that nonlinear optomechanical readout of thermally driven motion in these devices should be observable for T $> 50 $ mK, and that measurement of phonon shot noise is achievable.
Institute of Scientific and Technical Information of China (English)
张戈
2015-01-01
We studies the issue raised by Reference[3],according to appropriate assumptions and other smooth conditions,With a more simple method,Proved that asymptotic existence of quasi likelihood equations in Quasi-likelihood nonlinear model ,and proved the convergence rate of the solution.%在适当假定及其它一些光滑条件下,用更为简便的方法证明了拟似然非线性模型的拟似然方程解的渐近存在性,并且求出了该解收敛于真值的速度.
Quantitative assessment of diffusional kurtosis anisotropy.
Glenn, G Russell; Helpern, Joseph A; Tabesh, Ali; Jensen, Jens H
2015-04-01
Diffusional kurtosis imaging (DKI) measures the diffusion and kurtosis tensors to quantify restricted, non-Gaussian diffusion that occurs in biological tissue. By estimating the kurtosis tensor, DKI accounts for higher order diffusion dynamics, when compared with diffusion tensor imaging (DTI), and consequently can describe more complex diffusion profiles. Here, we compare several measures of diffusional anisotropy which incorporate information from the kurtosis tensor, including kurtosis fractional anisotropy (KFA) and generalized fractional anisotropy (GFA), with the diffusion tensor-derived fractional anisotropy (FA). KFA and GFA demonstrate a net enhancement relative to FA when multiple white matter fiber bundle orientations are present in both simulated and human data. In addition, KFA shows net enhancement in deep brain structures, such as the thalamus and the lenticular nucleus, where FA indicates low anisotropy. Thus, KFA and GFA provide additional information relative to FA with regard to diffusional anisotropy, and may be particularly advantageous for the assessment of diffusion in complex tissue environments.
Strong side of weak topological insulators
Ringel, Zohar; Kraus, Yaacov E.; Stern, Ady
2012-07-01
Three-dimensional topological insulators are classified into “strong” (STI) and “weak” (WTI) according to the nature of their surface states. While the surface states of the STI are topologically protected from localization, this does not hold for the WTI. In this work, we show that the surface states of the WTI are actually protected from any random perturbation that does not break time-reversal symmetry, and does not close the bulk energy gap. Consequently, the conductivity of metallic surfaces in the clean system remains finite even in the presence of strong disorder of this type. In the weak disorder limit, the surfaces are found to be perfect metals, and strong surface disorder only acts to push the metallic surfaces inwards. We find that the WTI differs from the STI primarily in its anisotropy, and that the anisotropy is not a sign of its weakness but rather of its richness.
Statistical Anisotropy from Anisotropic Inflation
Soda, Jiro
2012-01-01
We review an inflationary scenario with the anisotropic expansion rate. An anisotropic inflationary universe can be realized by a vector field coupled with an inflaton, which can be regarded as a counter example to the cosmic no-hair conjecture. We show generality of anisotropic inflation and derive a universal property. We formulate cosmological perturbation theory in anisotropic inflation. Using the formalism, we show anisotropic inflation gives rise to the statistical anisotropy in primordial fluctuations. We also explain a method to test anisotropic inflation using the cosmic microwave background radiation (CMB).
2016-07-01
Advanced Research Projects Agency (DARPA) Dynamics-Enabled Frequency Sources (DEFYS) program is focused on the convergence of nonlinear dynamics and...Early work in this program has shown that nonlinear dynamics can provide performance advantages. However, the pathway from initial results to...dependent nonlinear stiffness observed in these devices. This work is ongoing, and will continue through the final period of this program . Reference 9
Formation of Magnetic Anisotropy by Lithography.
Kim, Si Nyeon; Nam, Yoon Jae; Kim, Yang Doo; Choi, Jun Woo; Lee, Heon; Lim, Sang Ho
2016-05-24
Artificial interface anisotropy is demonstrated in alternating Co/Pt and Co/Pd stripe patterns, providing a means of forming magnetic anisotropy using lithography. In-plane hysteresis loops measured along two principal directions are explained in depth by two competing shape and interface anisotropies, thus confirming the formation of interface anisotropy at the Co/Pt and Co/Pd interfaces of the stripe patterns. The measured interface anisotropy energies, which are in the range of 0.2-0.3 erg/cm(2) for both stripes, are smaller than those observed in conventional multilayers, indicating a decrease in smoothness of the interfaces when formed by lithography. The demonstration of interface anisotropy in the Co/Pt and Co/Pd stripe patterns is of significant practical importance, because this setup makes it possible to form anisotropy using lithography and to modulate its strength by controlling the pattern width. Furthermore, this makes it possible to form more complex interface anisotropy by fabricating two-dimensional patterns. These artificial anisotropies are expected to open up new device applications such as multilevel bits using in-plane magnetoresistive thin-film structures.
Surface magnetic anisotropy in amorphous alloys
Energy Technology Data Exchange (ETDEWEB)
Tejedor, M.; Rubio, H.; Elbaile, L.; Iglesias, R. (Univ. de Oviedo (Spain). Dept. de Fisica)
1993-11-01
The total in-plane magnetic anisotropy and the in-plane surface magnetic anisotropy constants have been measured in nearly-zero magnetostrictive amorphous ribbons in as-quenched state. The magnetostatic energy of a two-dimensional square-lattice of parallelepipeds or ellipsoids, whose dimensions are determined by the parameters characterizing the roughness, is evaluated. From the results obtained, they can conclude that the in-plane surface anisotropy can be magnetostatic in origin but it has little influence on the total in-plane magnetic anisotropy of the ribbon.
Strongly Scale-dependent Non-Gaussianity
Riotto, Antonio
2011-01-01
We discuss models of primordial density perturbations where the non-Gaussianity is strongly scale-dependent. In particular, the non-Gaussianity may have a sharp cut-off and be very suppressed on large cosmological scales, but sizeable on small scales. This may have an impact on probes of non-Gaussianity in the large-scale structure and in the cosmic microwave background radiation anisotropies.
Nayfeh, Ali Hasan
1995-01-01
Nonlinear Oscillations is a self-contained and thorough treatment of the vigorous research that has occurred in nonlinear mechanics since 1970. The book begins with fundamental concepts and techniques of analysis and progresses through recent developments and provides an overview that abstracts and introduces main nonlinear phenomena. It treats systems having a single degree of freedom, introducing basic concepts and analytical methods, and extends concepts and methods to systems having degrees of freedom. Most of this material cannot be found in any other text. Nonlinear Oscillations uses sim
Yoshida, Zensho
2010-01-01
This book gives a general, basic understanding of the mathematical structure "nonlinearity" that lies in the depths of complex systems. Analyzing the heterogeneity that the prefix "non" represents with respect to notions such as the linear space, integrability and scale hierarchy, "nonlinear science" is explained as a challenge of deconstruction of the modern sciences. This book is not a technical guide to teach mathematical tools of nonlinear analysis, nor a zoology of so-called nonlinear phenomena. By critically analyzing the structure of linear theories, and cl
Nanda, Sudarsan
2013-01-01
"Nonlinear analysis" presents recent developments in calculus in Banach space, convex sets, convex functions, best approximation, fixed point theorems, nonlinear operators, variational inequality, complementary problem and semi-inner-product spaces. Nonlinear Analysis has become important and useful in the present days because many real world problems are nonlinear, nonconvex and nonsmooth in nature. Although basic concepts have been presented here but many results presented have not appeared in any book till now. The book could be used as a text for graduate students and also it will be useful for researchers working in this field.
Rajapitamahuni, Anil; Zhang, Le; Singh, Vijay; Burton, John; Koten, Mak; Shield, Jeffrey; Tsymbal, Evgeny; Hong, Xia
We report a unusual giant enhancement of in-plane magnetocrystalline anisotropy (MCA) in ultrathin colossal magnetoresistive oxide films due to 1D nanoscale periodic depth modulation. High quality epitaxial thin films of La0.67Sr0.33MnO3 (LSMO) of thickness 6 nm were grown on (001) SrTiO3 substrates via off-axis radio frequency magnetron sputtering. The top 2 nm of LSMO films are patterned into periodic nano-stripes using e-beam lithography and reactive ion etching. The resulting structure consists of nano-stripes of 2 nm height and 100-200 nm width on top of a 4 nm thick continuous base layer. We employed planar Hall effect measurements to study the in-plane magnetic anisotropy of the unpatterned and nanopatterned films. The unpatterned films show a biaxial anisotropy with easy axis along [110]. The extracted anisotropy energy density is ~1.1 x 105 erg/cm3, comparable to previously reported values. In the nanopatterned films, a strong uniaxial anisotropy is developed along one of the biaxial easy axes. The corresponding anisotropy energy density is ~5.6 x 106 erg/cm3 within the nano-striped volume, comparable to that of Co. We attribute the observed uniaxial MCA to MnO6 octahedral rotations/tilts and the enhancement in the anisotropy energy density to the strain gradient within the nano-stripes.
Energy Technology Data Exchange (ETDEWEB)
Liu, Ruo-Yu; Wang, Xiang-Yu [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Taylor, Andrew M. [Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland); Lemoine, Martin [Institut d' Astrophysique de Paris, CNRS, UPMC, 98 bis Boulevard Arago, F-75014 Paris (France); Waxman, Eli, E-mail: lemoine@iap.fr [Physics Faculty, Weizmann Institute, P.O. Box 26, Rehovot 7600 (Israel)
2013-10-20
The joint analysis of anisotropy signals and chemical composition of ultra-high-energy cosmic rays offers strong potential for shedding light on the sources of these particles. Following up on an earlier idea, this paper studies the anisotropies produced by protons of energy >E/Z, assuming that anisotropies at energy >E have been produced by nuclei of charge Z, which share the same magnetic rigidity. We calculate the number of secondary protons produced through photodisintegration of the primary heavy nuclei. Making the extreme assumption that the source does not inject any proton, we find that the source(s) responsible for anisotropies such as reported by the Pierre Auger Observatory should lie closer than ∼20-30, 80-100, and 180-200 Mpc if the anisotropy signal is mainly composed of oxygen, silicon, and iron nuclei, respectively. A violation of this constraint would otherwise result in the secondary protons forming a more significant anisotropy signal at lower energies. Even if the source were located closer than this distance, it would require an extraordinary metallicity ∼> 120, 1600, and 1100 times solar metallicity in the acceleration zone of the source, for oxygen, silicon, and iron, respectively, to ensure that the concomitantly injected protons do not produce a more significant low-energy anisotropy. This offers interesting prospects for constraining the nature and the source of ultra-high-energy cosmic rays with the increase in statistics expected from next-generation detectors.
Nonlinearities of biopolymer gels increase the range of force transmission
Xu, Xinpeng; Safran, Samuel A.
2015-09-01
We present a model of biopolymer gels that includes two types of elastic nonlinearities, stiffening under extension and softening (due to buckling) under compression, to predict the elastic anisotropy induced by both external as well as internal (e.g., due to cell contractility) stresses in biopolymer gels. We show how the stretch-induced anisotropy and the strain-stiffening nonlinearity increase both the amplitude and power-law range of transmission of internal, contractile, cellular forces, and relate this to recent experiments.
Optimization of artificial flockings by means of anisotropy measurements
Makiguchi, Motohiro
2010-01-01
An effective procedure to determine the optimal parameters appearing in artificial flockings is proposed in terms of optimization problems. We numerically examine genetic algorithms (GAs) to determine the optimal set of such parameters such as the weights for three essential interactions in BOIDS by Reynolds (1987) under `zero-collision' and `no-breaking-up' constraints. As a fitness function (the energy function) to be maximized by the GA, we choose the so-called the $\\textyen gamma$-value of anisotropy which can be observed empirically in typical flocks of starling. We confirm that the GA successfully finds the solution having a large $\\textyen gamma$-value leading-up to a strong anisotropy. The numerical experience shows that the procedure might enable us to make more realistic and efficient artificial flocking of starling even in our personal computers.
Microelectromechanical Maltese-cross metamaterial with tunable terahertz anisotropy
Zhu, W. M.; Liu, A. Q.; Bourouina, T.; Tsai, D. P.; Teng, J. H.; Zhang, X. H.; Lo, G. Q.; Kwong, D. L.; Zheludev, N. I.
2012-12-01
Dichroic polarizers and waveplates exploiting anisotropic materials have vast applications in displays and numerous optical components, such as filters, beamsplitters and isolators. Artificial anisotropic media were recently suggested for the realization of negative refraction, cloaking, hyperlenses, and controlling luminescence. However, extending these applications into the terahertz domain is hampered by a lack of natural anisotropic media, while artificial metamaterials offer a strong engineered anisotropic response. Here we demonstrate a terahertz metamaterial with anisotropy tunable from positive to negative values. It is based on the Maltese-cross pattern, where anisotropy is induced by breaking the four-fold symmetry of the cross by displacing one of its beams. The symmetry breaking permits the excitation of a Fano mode active for one of the polarization eigenstates controlled by actuators using microelectromechanical systems. The metamaterial offers new opportunities for the development of terahertz variable waveplates, tunable filters and polarimetry.
3D analyses of cavitation instabilities accounting for plastic anisotropy
DEFF Research Database (Denmark)
Legarth, Brian Nyvang; Tvergaard, Viggo
2010-01-01
, and the main focus is on the effect of different degrees of plastic anisotropy. Loading cases are considered, where all the macroscopic principal stresses differ. The numerical quasi‐static solutions are obtained by a full transient analysis of the equations of motion, in which the loading is applied so slowly......Full three dimensional cell model analyses are carried out for a solid containing a single small void, in order to determine the critical stress levels for the occurrence of cavitation instabilities. The material models applied are elastic‐viscoplastic, with a small rate‐hardening exponent...... that the quasi‐static solution is well approximated. A special procedure is used to strongly reduce the loading rate a little before the instability occurs. It is found that plastic anisotropy has a significant effect on the level of the critical stress for cavitation instabilities....
Anisotropy in the Ratchet Growth of PBX 9502
Energy Technology Data Exchange (ETDEWEB)
Schwarz, Ricardo Blum [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Liu, Cheng [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Thompson, Darla Graff [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-03-12
TATB-based compactions and composites are known to undergo “ratchet growth”, an irreversible volume increase that occurs upon heating or cooling of a specimen. Ratchet growth likely arises because the coefficient of thermal expansion of the TATB crystals is strongly anisotropic, but the exact mechanism is not well-understood. TATB crystals in solid, plastic-bonded, explosive PBX 9502 parts can have a preferred crystallographic orientation (texture) caused by the compaction process. As a result, the irreversible strain associated with PBX 9502 ratchet growth is anisotropic. The present paper relates the magnitude of ratchet growth to the crystalline anisotropy of the TATB crystals. The crystalline anisotropy is measured by x-ray diffraction and the ratchet growth is measured by a digital image-correlation technique.
Plastic anisotropy of straight and cross rolled molybdenum sheets
Energy Technology Data Exchange (ETDEWEB)
Oertel, C.-G. [Institut fuer Strukturphysik, Technische Universitaet Dresden, D-01062 Dresden (Germany)], E-mail: oertel@physik.tu-dresden.de; Huensche, I.; Skrotzki, W. [Institut fuer Strukturphysik, Technische Universitaet Dresden, D-01062 Dresden (Germany); Knabl, W.; Lorich, A.; Resch, J. [PLANSEE Metall GmbH, A-6600 Reutte, Tyrol (Austria)
2008-06-15
The microstructure, texture and mechanical properties of molybdenum sheets produced by different rolling processes were investigated by orientation imaging in the scanning electron microscope, X-ray diffraction and tensile tests, respectively. For comparable recrystallization degree of the sheets investigated, straight rolling with low reduction ratio produces {alpha}-fiber textures with a maximum at {l_brace}100{r_brace} <110>. At higher rolling degrees the maximum shifts to {l_brace}112{r_brace} <110>. Cross rolling increases the rotated cube component {l_brace}100{r_brace} <110>. The strong differences in the texture measured are reflected in the plastic anisotropy characterized by differences in the yield stress and Lankford parameter which were measured along directions in the rolling plane at angles of 0 deg., 45 deg. and 90 deg. with the rolling direction. The Taylor-Bishop-Hill theory is used successfully to qualitatively explain the plastic anisotropy.
Nonlinear approaches in engineering applications 2
Jazar, Reza N
2013-01-01
Provides updated principles and applications of the nonlinear approaches in solving engineering and physics problems Demonstrates how nonlinear approaches may open avenues to better, safer, cheaper systems with less energy consumption Has a strong emphasis on the application, physical meaning, and methodologies of nonlinear approaches in different engineering and science problems
Nonlinear Optics: Principles and Applications
DEFF Research Database (Denmark)
Rottwitt, Karsten; Tidemand-Lichtenberg, Peter
As nonlinear optics further develops as a field of research in electromagnetic wave propagation, its state-of-the-art technologies will continue to strongly impact real-world applications in a variety of fields useful to the practicing scientist and engineer. From basic principles to examples...... of applications, Nonlinear Optics: Principles and Applications effectively bridges physics and mathematics with relevant applied material for real-world use. The book progresses naturally from fundamental aspects to illustrative examples, and presents a strong theoretical foundation that equips the reader...... and matter, this text focuses on the physical understanding of nonlinear optics, and explores optical material response functions in the time and frequency domain....
Terahertz Nonlinearity in Graphene Plasmons
Jadidi, Mohammad M; Winnerl, Stephan; Sushkov, Andrei B; Drew, H Dennis; Murphy, Thomas E; Mittendorff, Martin
2015-01-01
Sub-wavelength graphene structures support localized plasmonic resonances in the terahertz and mid-infrared spectral regimes. The strong field confinement at the resonant frequency is predicted to significantly enhance the light-graphene interaction, which could enable nonlinear optics at low intensity in atomically thin, sub-wavelength devices. To date, the nonlinear response of graphene plasmons and their energy loss dynamics have not been experimentally studied. We measure and theoretically model the terahertz nonlinear response and energy relaxation dynamics of plasmons in graphene nanoribbons. We employ a THz pump-THz probe technique at the plasmon frequency and observe a strong saturation of plasmon absorption followed by a 10 ps relaxation time. The observed nonlinearity is enhanced by two orders of magnitude compared to unpatterned graphene with no plasmon resonance. We further present a thermal model for the nonlinear plasmonic absorption that supports the experimental results.
Strong monotonicity for analytic ordinary differential equations
Directory of Open Access Journals (Sweden)
Sebastian Walcher
2009-09-01
Full Text Available We present a necessary and sufficient criterion for the flow of an analytic ordinary differential equation to be strongly monotone; equivalently, strongly order-preserving. The criterion is given in terms of the reducibility set of the derivative of the right-hand side. Some applications to systems relevant in biology and ecology, including nonlinear compartmental systems, are discussed.
Magnetic anisotropies in ferromagnetic and exchange-coupled systems on rippled surfaces
Energy Technology Data Exchange (ETDEWEB)
Liedke, Maciej Oskar; Liedke, Bartosz; Marko, Daniel; Keller, Adrian; Muecklich, Arndt; Facsko, Stefan; Fassbender, Juergen [FZ Dresden-Rossendorf, FWI, Dresden (Germany); Cizmar, Erik; Zvyagin, Sergei; Wosnitza, Joachim [FZ Dresden-Rossendorf, HLD, Dresden (Germany)
2008-07-01
The influence of a surface and interface modulation on the magnetic properties of ferromagnetic materials (Py, Fe and Co) and an exchange bias system (Py/FeMn) is studied. A periodic surface modulation (the so-called ripples) is achieved by low energy ion erosion. Subsequently the magnetic stack is deposited. Due to the film morphology a strong uniaxial anisotropy is induced in the ferromagnetic layers, which is fixed in its orientation along ripples elongation. In the case of the exchange bias system the direction of the induced unidirectional anisotropy can be varied by means of different field annealing cycles. For all mutual orientations both anisotropy contributions are superimposed independently. The angular dependence of the magnetization reversal behavior can be described perfectly by a coherent rotation model. In addition, the magnitude of the uniaxial and the unidirectional anisotropy scales with the step density or wave length of the rippled substrate, which is in full agreement with theoretical predictions.
Extremely high thermal conductivity anisotropy of double-walled carbon nanotubes
Directory of Open Access Journals (Sweden)
Zhaoji Ma
2017-06-01
Full Text Available Based on molecular dynamics simulations, we reveal that double-walled carbon nanotubes can possess an extremely high anisotropy ratio of radial to axial thermal conductivities. The mechanism is basically the same as that for the high thermal conductivity anisotropy of graphene layers - the in-plane strong sp2 bonds lead to a very high intralayer thermal conductivity while the weak van der Waals interactions to a very low interlayer thermal conductivity. However, different from flat graphene layers, the tubular structures of carbon nanotubes result in a diameter dependent thermal conductivity. The smaller the diameter, the larger the axial thermal conductivity but the smaller the radial thermal conductivity. As a result, a DWCNT with a small diameter may have an anisotropy ratio of thermal conductivity significantly higher than that for graphene layers. The extremely high thermal conductivity anisotropy allows DWCNTs to be a promising candidate for thermal management materials.
Extremely high thermal conductivity anisotropy of double-walled carbon nanotubes
Ma, Zhaoji; Guo, Zhengrong; Zhang, Hongwei; Chang, Tienchong
2017-06-01
Based on molecular dynamics simulations, we reveal that double-walled carbon nanotubes can possess an extremely high anisotropy ratio of radial to axial thermal conductivities. The mechanism is basically the same as that for the high thermal conductivity anisotropy of graphene layers - the in-plane strong sp2 bonds lead to a very high intralayer thermal conductivity while the weak van der Waals interactions to a very low interlayer thermal conductivity. However, different from flat graphene layers, the tubular structures of carbon nanotubes result in a diameter dependent thermal conductivity. The smaller the diameter, the larger the axial thermal conductivity but the smaller the radial thermal conductivity. As a result, a DWCNT with a small diameter may have an anisotropy ratio of thermal conductivity significantly higher than that for graphene layers. The extremely high thermal conductivity anisotropy allows DWCNTs to be a promising candidate for thermal management materials.
Geotail observations of temperature anisotropy of the two-component protons in the dusk plasma sheet
Directory of Open Access Journals (Sweden)
M. N. Nishino
2007-03-01
Full Text Available In search for clues towards the understanding of the cold plasma sheet formation under northward IMF, we study the temperature anisotropy of the two-component protons in the plasma sheet near the dusk low-latitude boundary observed by the Geotail spacecraft. The two-component protons result from mixing of the cold component from the solar wind and the hot component of the magnetospheric origin, and may be the most eloquent evidence for the transport process across the magnetopause. The cold component occasionally has a strong anisotropy in the dusk flank, and the sense of the anisotropy depends on the observed locations: the parallel temperature is enhanced in the tail flank while the perpendicular temperature is enhanced on the dayside. The hot component is nearly isotropic in the tail while the perpendicular temperature is enhanced on the dayside. We discuss possible mechanism that can lead to the observed temperature anisotropies.
Tayon, W.; Shenoy, R.; Bird, R.; Hafley, R.; Redding, M.
2014-01-01
A test block of Inconel (IN) 718 was fabricated using electron beam freeform fabrication (EBF(sup 3)) to examine how the EBF(sup 3) deposition process affects the microstructure, crystallographic texture, and mechanical properties of IN 718. Tests revealed significant anisotropy in the elastic modulus for the as-deposited IN 718. Subsequent tests were conducted on specimens subjected to a heat treatment designed to decrease the level of anisotropy. Electron backscatter diffraction (EBSD) was used to characterize crystallographic texture in the as-deposited and heat treated conditions. The anisotropy in the as-deposited condition was strongly affected by texture as evidenced by its dependence on orientation relative to the deposition direction. Heat treatment resulted in a significant improvement in modulus of the EBF(sup 3) product to a level nearly equivalent to that for wrought IN 718 with reduced anisotropy; reduction in texture through recrystallization; and production of a more homogeneous microstructure.
Anisotropy and Magnetostriction in Cobalt-Modified Magnetite: A Crystal Field Approach
Nlebedim, Cajetan; Jiles, David
2013-03-01
The anisotropy and magnetostrictive properties of magnetite are altered by the introduction of cobalt ions into the spinel crystal lattice. 4% of Co2+ substituted for Fe2+ changes both the sign and magnitude of magnetocrystalline anisotropy coefficient. Such strong dependence can be useful for tailoring the properties of cobalt-iron oxides for applications. This is especially important, considering that cobalt ferrite materials prepared for magnetostrictive, multiferroic and other related applications often deviate from targeted or stoichiometric compositions. In this study, magnetite has been systematically modified by substitution of cobalt. The changes in anisotropy and magnetostriction have been studied and can be explained using the single ion model. The agreement between the trend observed in this experimental investigation and previous theoretical studies is noteworthy. The variation in anisotropy and magnetostriction will be presented on the basis of two competing factors; the unquenched orbital angular momentum of Co2+ and changes in the crystal field due to Co2+ substitution.
Boettcher, Igor
2016-01-01
We illuminate the intriguing role played by spatial anisotropy in three-dimensional Luttinger semimetals featuring quadratic band touching and long-range Coulomb interactions. We observe the anisotropy to be subject to an exceptionally slow renormalization group (RG) evolution so that it can be considered approximately constant when computing the impact of quantum fluctuations on the remaining couplings of the system. Using perturbative RG we then study the competition of all local short-range interactions that are generated from the long-range interactions for fixed anisotropy. Two main effects come to light for sufficiently strong anisotropy. First, the three-dimensional system features an Abrikosov non-Fermi liquid ground state. Second, there appear qualitatively new fixed points which describe quantum phase transitions into phases with nemagnetic orders - higher-rank tensor orders that break time-reversal symmetry, and thus have both nematic and magnetic character. In real materials these phases may be re...
Measuring the Alfvenic Nature of the Interstellar Medium: Velocity Anisotropy Revisited
Burkhart, Blakesley; Leao, I C; de Medeiros, J R; Esquivel, A
2014-01-01
The dynamics of the interstellar medium (ISM) are strongly affected by turbulence, which shows increased anisotropy in the presence of a magnetic field. We expand upon the Esquivel & Lazarian method to estimate the Alfven Mach number using the structure function anisotropy in velocity centroid data from position-position-velocity maps. We utilize 3D magnetohydrodynamic (MHD) simulations of fully developed turbulence, with a large range of sonic and Alfvenic Mach numbers, to produce synthetic observations of velocity centroids with observational characteristics such as thermal broadening, cloud boundaries, noise, and radiative transfer effects of carbon monoxide. In addition, we investigate how the resulting anisotropy-Alfven Mach number dependency found in Esquivel & Lazarian (2011) might change when taking the second moment of the position-position-velocity cube or when using different expressions to calculate the velocity centroids. We find that the degree of anisotropy is related primarily to the m...
Measurements of the anisotropy in permalloy
Eijkel, Kees J.
1988-01-01
A measurement system is described, which accurately determines the anisotropy field H/sub k/ and the orientation of the easy-axis in a permalloy film or in any material showing magnetization induced resistance anisotropy. An accuracy of 0.1% in H/sub k/ and 0.1 degrees in easy-axis orientation is re
Ha, Yoonhae; Jung, Haemyeong; Raymond, Loren
2016-04-01
Seismic anisotropy has been observed in many subduction zones. During subduction of slab, the oceanic crust changes to blueschist and eclogite. Since minerals in blueschist are very anisotropic elastically, seismic properties in the subducting slab can be attributed to the lattice preferred orientation (LPO) of these minerals. We studied microstructures and seismic properties of blueschist and eclogite from Ring Mt. and Jenner in California. Blueschist samples are mainly composed of glaucophane, epidote and phengite. Eclogite samples are mostly composed of omphacite, glaucophane, epidote and garnet. We determined LPOs of minerals using SEM/EBSD and calculated seismic properties of minerals and whole rocks. LPOs of glaucophane showed [001] axes are aligned subparallel to lineation, and both (110) poles and [100] axes subnormal to foliation. Glaucophane in samples from Jenner, however, exhibited [001] axes forming a girdle subparallel to lineation. Seismic anisotropy of glaucophane was stronger in samples from Ring Mt. than those from Jenner. Epidote showed [001] axes are aligned subnormal to foliation and (110) and (010) poles subparallel to lineation. LPOs of phengite were characterized by a maximum of [001] axes normal to foliation, with (110) and (010) poles and [100] axes aligning in a girdle parallel to foliation. Phengite showed the strongest seismic anisotropy among major minerals. LPOs of omphacite showed [001] axes are aligned subparallel to lineation and [010] axes subnormal to foliation. Seismic anisotropy of omphacite were very weak. Blueschist from Ring Mt. showed stronger seismic anisotropy than those from Jenner. Especially, blueschist including abundant phengite showed very strong seismic anisotropy (AVP=30%, max.AVS=23%). Eclogite showed much weaker seismic anisotropy (AVP=7%, max.AVS=6%) than blueschist (AVP=12-30%, max.AVS=9-23%). Therefore, strong seismic anisotropy observed in subduction zone can be more affected by blueschist than eclogite.
Optical and diamagnetic anisotropy of graphene oxide
Exarhos, A. L.; Vora, P. M.; Lou, Z.; Johnson, A. T.; Kikkawa, J. M.
2009-03-01
We have recently shown that graphene oxide (GO) emits a broad photoluminescence (PL) band in both solid and aqueous preparations. The origin of this PL is not yet well understood, but for absorptive and emissive optical processes originating in the two dimensional GO plane, one expects an in-plane polarization. Studies of optical anisotropy can therefore help to clarify the origin of the PL. Here we use a method of optical nanomagnetometry (Torrens, et al, JACS 129, p. 252 (2007)) to extract these quantities, also determining the magnetic anisotropy. We find that when aqueous preparations of GO are placed in a magnetic field, diamagnetically induced alignment leads to marked linear polarization anisotropy of absorbance and photoluminescence. By taking six optical measurements at each magnetic field, we are able to extract the intrinsic polarization anisotropies of optical absorption and emission of GO flakes and to quantify the orbital diamagnetic anisotropy. We discuss how these quantities give insight into electronic delocalization in these systems.
Anisotropy in solar wind plasma turbulence.
Oughton, S; Matthaeus, W H; Wan, M; Osman, K T
2015-05-13
A review of spectral anisotropy and variance anisotropy for solar wind fluctuations is given, with the discussion covering inertial range and dissipation range scales. For the inertial range, theory, simulations and observations are more or less in accord, in that fluctuation energy is found to be primarily in modes with quasi-perpendicular wavevectors (relative to a suitably defined mean magnetic field), and also that most of the fluctuation energy is in the vector components transverse to the mean field. Energy transfer in the parallel direction and the energy levels in the parallel components are both relatively weak. In the dissipation range, observations indicate that variance anisotropy tends to decrease towards isotropic levels as the electron gyroradius is approached; spectral anisotropy results are mixed. Evidence for and against wave interpretations and turbulence interpretations of these features will be discussed. We also present new simulation results concerning evolution of variance anisotropy for different classes of initial conditions, each with typical background solar wind parameters.
Crystal preferred orientation of amphibole and implications for seismic anisotropy in the crust
Jung, Haemyeong
2016-04-01
Strong seismic anisotropy is often observed in the middle to lower crust and it has been considered to be originated from the crystal preferred orientation (CPO) of anisotropic minerals such as amphibole. Amphibolite is one of the dominant rocks in the middle to lower crust. In this study, crystal preferred orientations of hornblende in amphibolites at Yeoncheon and Chuncheon areas in South Korea were determined by using the electron backscattered diffraction (EBSD)/SEM with HKL Channel 5 software. In Yeoncheon area, hornblende showed two types of CPOs. Type-I CPO is characterized as (100) poles of hornblende aligned subnormal to foliation and [001] axes aligned subparallel to lineation. Type-II CPO is characterized as (100) poles of hornblende aligned subnormal to foliation and (010) poles aligned subparallel to lineation (refer to Ko and Jung, 2015, Nature Communications). In Chuncheon area, three types of CPOs of hornblende were observed. In addition to the type-I and -II CPOs described above, type-III CPO of hornblende was observed in Chuncheon area and it is characterized as (100) poles of hornblende aligned subnormal to foliation and both [001] axes and (010) poles aligned as a girdle subparallel to foliation. Using the observed CPO and the single crystal elastic constant of hornblende, seismic anisotropy of hornblende was calculated. Seismic anisotropy of P-wave was strong in the range of 10.2 - 13.5 %. Seismic anisotropy of S-wave was also strong in the range of 6.9 - 11.2 %. These results show that hornblende deformed in nature can produce a strong CPO, resulting in a strong seismic anisotropy in the middle to lower crust. Taking into account of the CPO of plagioclase in the rock, seismic anisotropies of whole rock turned out to be maximum P-wave anisotropy (Vp) of 9.8% and maximum S-wave anisotropy (Vs) of 8.2%. Therefore, strong seismic anisotropy found in the middle to lower crust in nature can be attributed to the CPO of hornblende in amphibolite.
Non-Gaussianity of Large-Scale CMB Anisotropies beyond Perturbation Theory
Bartolo, N; Riotto, Antonio
2005-01-01
We compute the fully non-linear Cosmic Microwave Background (CMB) anisotropies on scales larger than the horizon at last-scattering in terms of only the curvature perturbation, providing a generalization of the linear Sachs-Wolfe effect at any order in perturbation theory. We show how to compute the $n$-point connected correlation functions of the large-scale CMB anisotropies for generic primordial seeds provided by standard slow-roll inflation as well as the curvaton and other scenarios for the generation of cosmological perturbations. As an application of our formalism, we compute the three- and four-point connected correlation functions whose detection in future CMB experiments might be used to assess the level of primordial non-Gaussianity, giving the theoretical predictions for the parameters of quadratic and cubic non-linearities f_NL and g_NL.
Skewness in the Cosmic Microwave Background Anisotropy from Inflationary Gravity Wave Background
Bharadwaj, S; Souradeep, T; Bharadwaj, Somnath; Munshi, Dipak; Souradeep, Tarun
1997-01-01
In the context of inflationary scenarios, the observed large angle anisotropy of the Cosmic Microwave Background (CMB) temperature is believed to probe the primordial metric perturbations from inflation. Although the perturbations from inflation are expected to be gaussian random fields, there remains the possibility that nonlinear processes at later epochs induce ``secondary'' non-gaussian features in the corresponding CMB anisotropy maps. The non-gaussianity induced by nonlinear gravitational instability of scalar (density) perturbations has been investigated in existing literature. In this paper, we highlight another source of non-gaussianity arising out of higher order scattering of CMB photons off the metric perturbations. We provide a simple and elegant formalism for deriving the CMB temperature fluctuations arising due to the Sachs-Wolfe effect beyond the linear order. In particular, we derive the expression for the second order CMB temperature fluctuations. The multiple scattering effect pointed out i...
Ciattoni, Alessandro
2014-01-01
Strong nonlinear optical mechanisms operating in a miniaturized environment have a key role in photonics since they allow complex and versatile light manipulation within subwavelength devices. On the other hand, due to its two-dimensional planar geometry, graphene can easily be embedded within miniaturized structures and has fascinating linear and nonlinear optical properties arising from its relativistic electron dynamics. However, very few light steering graphene-based setups with a strong nonlinear behavior have been proposed since, due to its intrinsic planar localization, graphene nonlinearity has to be exploited through novel schemes not available in standard bulk nonlinear optics. Here we show that an active cavity hosting a graphene sheet, when tuned near its lasing threshold, is able to isolate the spatially localized graphene nonlinearity thus producing a very strong nonlinear device response with multi-valued features. The proposed strategy for exploiting graphene nonlinearity through its baring co...
Seepage Anisotropy of Heterogeneous Body
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Ore dumps are heterogeneous bodies with anisotropic seepage characteristics because of the ore segregation.In an indoor experiment, a dump was constructed with three strata, where the horizontal and vertical seepage experiments were carried out.Horizontals flow are regarded as phreatic plan flows without penetration.Its seepage law satifies the Dupuit equation.With parallel lay seepage model, the equivalent seepage coefficient in the horizontal flow was obtained and was equivalent to the weighted mean of the seepage coefficient of each stratum.An unsaturated flow appeared in the vertical experiment, with a hydraulic gradient of 1.The vertical flow was equivalent to the seepage model that moved in vertical bedding; its equivalent seepage coefficient depended on the stratum with the minimum seepage coefficient.That the experiment showed clear anisotropy in a heterogeneous body was obvious with an anisotropic coefficient between 63 and 155, which is 25 to 100 times larger than that of a homogeneous body.
CMB anisotropy science: a review
Challinor, Anthony
2012-01-01
The cosmic microwave background (CMB) provides us with our most direct observational window to the early universe. Observations of the temperature and polarization anisotropies in the CMB have played a critical role in defining the now-standard cosmological model. In this contribution we review some of the basics of CMB science, highlighting the role of observations made with ground-based and balloon-borne Antarctic telescopes. Most of the ingredients of the standard cosmological model are poorly understood in terms of fundamental physics. We discuss how current and future CMB observations can address some of these issues, focusing on two directly relevant for Antarctic programmes: searching for gravitational waves from inflation via B-mode polarization, and mapping dark matter through CMB lensing.
Directory of Open Access Journals (Sweden)
Rasolofosaon P.
2006-12-01
Full Text Available This summary contains formulas (*** which can not be displayed on the screenA general principle outlined by P. Curie (1894 regarding the influence of symmetry in physical phenomena states, in modern language, that the symmetry group of the causes is a sub-group of the symmetry group of the effects. For instance, regarding stress-induced seismic anisotropy, the most complex symmetry exhibited by an initially isotropic medium when tri-axially stressed is orthorhombic, or orthotropic, symmetry characterized by three symmetry planes mutually perpendicular (Nur, 1971. In other respects, Schwartz et al. (1994 demonstrated that two very different rock models, namely a cracked model and a weakly consolidated granular model, always lead to elliptical anisotropy when uniaxially stressed. The addressed questions are : Is this result true for any rock model? and more generally : Do initially isotropic rock form a well-defined sub-set of orthorhombic media when triaxially stressed?Under the hypothesis of 3rd order nonlinear isotropic hyperelasticity (i. e. , no hysteresis and existence of an elastic energy function developed to the 3rd order in the strain components it is demonstrated that the qP-wave stress-induced anisotropy is always ellipsoidal, for any strength of anisotropy. For instance point sources generate ellipsoidal qP-wave fronts. This result is general and absolutely independent of the rock model, that is to say independent of the causes of nonlinearity, as far as the initial assumptions are verified. This constitutes the main result of this paper. Thurston (1965 pointed out that an initially isotropic elastic medium, when non-isotropically pre-stressed, is never strictly equivalent to an unstressed anisotropic crystal. For instance the components of the stressed elastic tensor lack the familiar symmetry with respect to indices permutation. This would prohibit Voigt's notation of contracted indices. However if the magnitude of the components of
Institute of Scientific and Technical Information of China (English)
谷峰
2001-01-01
使用新的分析技巧，研究了一致光滑Banach空间中ψ强增生算子方程的解和ψ强伪压缩算子不动点的Ishikawa迭代逼近问题，改进和扩展了近期的许多相关结果.%In this artice, by virtue of some analysis techniques, we have studied approximation problem of Ishikawa iterative sequence for the solution of ψ-strongly accretive operators and the fixed point.of p-strongly pseudo-contractive operators in uniformly smooth Banach spaces. Our results improve and extend the recent corresponding results.
Zhu, Hong-Ming; Pen, Ue-Li; Chen, Xuelei; Yu, Hao-Ran
2016-01-01
We present a direct approach to non-parametrically reconstruct the linear density field from an observed non-linear map. We solve for the unique displacement potential consistent with the non-linear density and positive definite coordinate transformation using a multigrid algorithm. We show that we recover the linear initial conditions up to $k\\sim 1\\ h/\\mathrm{Mpc}$ with minimal computational cost. This reconstruction approach generalizes the linear displacement theory to fully non-linear fields, potentially substantially expanding the BAO and RSD information content of dense large scale structure surveys, including for example SDSS main sample and 21cm intensity mapping.
Boyd, Robert W
2013-01-01
Nonlinear Optics is an advanced textbook for courses dealing with nonlinear optics, quantum electronics, laser physics, contemporary and quantum optics, and electrooptics. Its pedagogical emphasis is on fundamentals rather than particular, transitory applications. As a result, this textbook will have lasting appeal to a wide audience of electrical engineering, physics, and optics students, as well as those in related fields such as materials science and chemistry.Key Features* The origin of optical nonlinearities, including dependence on the polarization of light* A detailed treatment of the q
Nonlinear optomechanics with graphene
Shaffer, Airlia; Patil, Yogesh Sharad; Cheung, Hil F. H.; Wang, Ke; Vengalattore, Mukund
2016-05-01
To date, studies of cavity optomechanics have been limited to exploiting the linear interactions between the light and mechanics. However, investigations of quantum signal transduction, quantum enhanced metrology and manybody physics with optomechanics each require strong, nonlinear interactions. Graphene nanomembranes are an exciting prospect for realizing such studies due to their inherently nonlinear nature and low mass. We fabricate large graphene nanomembranes and study their mechanical and optical properties. By using dark ground imaging techniques, we correlate their eigenmode shapes with the measured dissipation. We study their hysteretic response present even at low driving amplitudes, and their nonlinear dissipation. Finally, we discuss ongoing efforts to use these resonators for studies of quantum optomechanics and force sensing. This work is supported by the DARPA QuASAR program through a Grant from the ARO.
Directory of Open Access Journals (Sweden)
József K. Tar
2004-05-01
Full Text Available In this paper the applicability of an adaptive control based on a novel branch ofComputational Cybernetics is illustrated for two different, imperfectly andinaccurately modeled particular physical sytems. One of them is a water tankstirring cold and hot water as input and releasing the mixture through a long pipe.The mass flow rate and the temperature are prescribed at the free end of the exitpipe while the taps at the input side can diretly be controlled. Due to theincompressibility of the fluid the variation of the mass flow rate of the output isimmediately observableat the pipe’s end and is related to the control action at theinput taps, while its effect on the temperature becomes measurable at the free endof the pipe only after a delay time needed for the fluid to flow through the pipe.This results in asymmetric and non-constant delay time. The other paradigm is thethermal decay of the molecular nitrogen during a throttling down process. As iswell known chemical reactions hav very drastic non-linearities and it is not easyto construct their “exact” or satisfacorily avccurate model. The fundamentalprinciples of this new branch of Computational Cybernetics are briefly presentedin the paper. To some extent it is similar to the traditional Soft Computing, but byusing a priori known, uniform, lucid structure of reduced size, it can evade theenormous structures so characteristic to the usual approach. Clumsydeterministic, semi-stochastic or stochastic machine learning is replaced bysimple, short, explicit algebraic procedures especially fit to real time applications.The costs of these advantages may manifest themselves in the expected limitationof the applicabilityof this new approach. However, the simulation resultsexemplify the applicability of the new method in the control of systems of strongnon-linearities and asymmetric delay time.
Communication: Solute Anisotropy Effects in Hydrated Anion and Neutral Clusters
Energy Technology Data Exchange (ETDEWEB)
Wen, Hui; Hou, Gao-Lei; Kathmann, Shawn M.; Valiev, Marat; Wang, Xue B.
2013-01-21
Specific ion effects in solvation processes are often rationalized in terms of spherically symmetric models involving an ion’s size, charge, and polarizability. The effects of permanent charge anisotropy, related to the polyatomic nature of complex solutes, are expected to play a role in solvation but the extent of their importance remains unexplored. In this work we provide compelling experimental and theoretical evidence that the anisotropic nature of complex polyoxyanion solutes can have a critical influence on the solvation process. Combined photoelectron spectroscopy and theoretical modeling results show that the electron binding energy (EBE) of IO3-(H2O)n (n = 0 - 12) clusters is characterized by an anomalous drop at n = 10. Such behavior is unprecedented for rigid solute molecules, and is related to the anisotropy of the neutral iodate radical that displays a strong selectivity to solvent configurations generated by the charged anion complex. These results highlight the significance of solute anisotropy and its potential impact on ion specificity and selectivity in aqueous environments.
Relativistic Plasma Polarizer: Impact of Temperature Anisotropy on Relativistic Transparency
Hazeltine, R. D.; Stark, David J.; Bhattacharjee, Chinmoy; Arefiev, Alexey V.; Toncian, Toma; Mahajan, S. M.
2015-11-01
3D particle-in-cell simulations demonstrate that the enhanced transparency of a relativistically hot plasma is sensitive to how the energy is partitioned between different degrees of freedom. We consider here the simplest problem: the propagation of a low amplitude pulse through a preformed relativistically hot anisotropic electron plasma to explore its intrinsic dielectric properties. We find that: 1) the critical density for propagation depends strongly on the pulse polarization, 2) two plasmas with the same density and average energy per electron can exhibit profoundly different responses to electromagnetic pulses, 3) the anisotropy-driven Weibel instability develops as expected; the timescales of the growth and back reaction (on anisotropy), however, are long enough that sufficient anisotropy persists for the entire duration of the simulation. This plasma can then function as a polarizer or a wave plate to dramatically alter the pulse polarization. This work was supported by the U.S. DOE Contract Nos. DE-FG02-04ER54742 and DE-AC05-06OR23100 (D. J. S.) and NNSA Contract No. DE-FC52-08NA28512.
Emergence of Anisotropy in Flock Simulations and Its Computational Analysis
Makiguchi, Motohiro; Inoue, Jun-Ichi
2010-03-01
In real flocks, it was revealed that the angular density of nearest neighbors shows a strong anisotropic structure of individuals by very recent extensive field studies [Ballerini et al, Proceedings of the National Academy of Sciences USA 105, pp. 1232-1237 (2008)]. In this paper, we show that this structure of anisotropy also emerges in an artificial flock simulation, namely, Boid simulation by Reynolds [C.W. Reynolds, Flocks, Herds, and Schools: A Distributed Behavioral Model, Computer Graphics, 21, pp. 25-34 (1987)]. To quantify the anisotropy, we evaluate a useful statistics, that is to say, the so-called γ-value which is defined as an inner product between the vector in the direction of the lowest angular density of flocks and the vector in the direction of the flock is moving. Our results concerning the emergence of the anisotropy through the γ-value might enable us to judge whether an optimal flock simulation seems to be realistic or not.
Radial orbital anisotropy and the Fundamental Plane of elliptical galaxies
Nipoti, C; Ciotti, L; Nipoti, Carlo; Londrillo, Pasquale; Ciotti, Luca
2002-01-01
The existence of the Fundamental Plane (FP) imposes strong constraints on the structure and dynamics of elliptical galaxies, and thus contains important information on the processes of their formation and evolution. Here we focus on the relations between the FP thinness and tilt and the amount of radial orbital anisotropy. By using N-body simulations of galaxy models characterized by observationally motivated density profiles, and also allowing for the presence of live, massive dark matter halos, we explore the impact of radial orbital anisotropy and instability on the FP properties. The numerical results confirm a previous semi--analytical finding: the requirement of stability matches almost exactly the thinness of the FP. In other words, galaxy models that are radially anisotropic enough to be found outside the observed FP (with their isotropic parent models lying on the FP) are unstable, and their end--products fall back on the FP itself. We also find that a systematic increase of radial orbit anisotropy w...
Anisotropy of Photopolymer Parts Made by Digital Light Processing
Monzón, Mario; Ortega, Zaida; Hernández, Alba; Paz, Rubén; Ortega, Fernando
2017-01-01
Digital light processing (DLP) is an accurate additive manufacturing (AM) technology suitable for producing micro-parts by photopolymerization. As most AM technologies, anisotropy of parts made by DLP is a key issue to deal with, taking into account that several operational factors modify this characteristic. Design for this technology and photopolymers becomes a challenge because the manufacturing process and post-processing strongly influence the mechanical properties of the part. This paper shows experimental work to demonstrate the particular behavior of parts made using DLP. Being different to any other AM technology, rules for design need to be adapted. Influence of build direction and post-curing process on final mechanical properties and anisotropy are reported and justified based on experimental data and theoretical simulation of bi-material parts formed by fully-cured resin and partially-cured resin. Three photopolymers were tested under different working conditions, concluding that post-curing can, in some cases, correct the anisotropy, mainly depending on the nature of photopolymer. PMID:28772426
Texture and anisotropy of ferroelectric bismuth titanate
Jones, Jacob Leo
Ferroelectric bismuth titanate, Na0.5Bi4.5 Ti4O15, is a piezoelectric ceramic used as an electromechanical sensor in high temperature environments (T piezoelectric constant, d33, is relatively low in randomly oriented ceramics. Crystallographic texturing is often employed to increase the piezoelectric constant because the spontaneous polarization axes of the grains are better aligned. This research distinguishes between the crystallographic texture induced to the grains from tape casting and crystallographic texture induced to the ferroelectric domains from electrical poling. Novel quantitative approaches describe texture of both types independently using conventional and synchrotron X-ray sources as well as time-of-flight neutron diffraction with multiple detectors. Furthermore, methods are developed to describe the combined effect of a ferroelectric texture superimposed on a paraelectric texture. Texture of the paraelectric crystallographic axes was induced by novel processing approaches. An alternative to using plate-shaped template particles was developed utilizing calcined powder. Paraelectric texture develops from particle settling and strong surface energy anisotropy during sintering. The 00l textures induced from this process are on the order of two to four multiples of a random distribution. These textures create property anisotropies between the casting plane and normal directions of 6.4 and 5.7 in piezoelectric d33 constant and remanent polarization, respectively. Texture of the ferroelectric crystallographic axes was induced by electrical poling at different temperatures and in different orientations. Ceramics with an initial paraelectric texture can exhibit greater change in the domain volume fractions during electrical poling than randomly oriented ceramics. This is demonstrated by applying novel quantitative approaches to reflection X-ray spectra from many sample directions. Because orthorhombic Na0.5Bi 4.5Ti4O15 has two ferroelectric domains that
Ruszczynski, Andrzej
2011-01-01
Optimization is one of the most important areas of modern applied mathematics, with applications in fields from engineering and economics to finance, statistics, management science, and medicine. While many books have addressed its various aspects, Nonlinear Optimization is the first comprehensive treatment that will allow graduate students and researchers to understand its modern ideas, principles, and methods within a reasonable time, but without sacrificing mathematical precision. Andrzej Ruszczynski, a leading expert in the optimization of nonlinear stochastic systems, integrates t
Borghi, M.; Castellan, C.; Signorini, S.; Trenti, A.; Pavesi, L.
2017-09-01
Silicon photonics is a technology based on fabricating integrated optical circuits by using the same paradigms as the dominant electronics industry. After twenty years of fervid development, silicon photonics is entering the market with low cost, high performance and mass-manufacturable optical devices. Until now, most silicon photonic devices have been based on linear optical effects, despite the many phenomenologies associated with nonlinear optics in both bulk materials and integrated waveguides. Silicon and silicon-based materials have strong optical nonlinearities which are enhanced in integrated devices by the small cross-section of the high-index contrast silicon waveguides or photonic crystals. Here the photons are made to strongly interact with the medium where they propagate. This is the central argument of nonlinear silicon photonics. It is the aim of this review to describe the state-of-the-art in the field. Starting from the basic nonlinearities in a silicon waveguide or in optical resonator geometries, many phenomena and applications are described—including frequency generation, frequency conversion, frequency-comb generation, supercontinuum generation, soliton formation, temporal imaging and time lensing, Raman lasing, and comb spectroscopy. Emerging quantum photonics applications, such as entangled photon sources, heralded single-photon sources and integrated quantum photonic circuits are also addressed at the end of this review.
Strong anisotropic thermal conductivity of monolayer WTe2
Ma, Jinlong; Chen, Yani; Han, Zheng; Li, Wu
2016-12-01
Tungsten ditelluride (WTe2) has attracted increasing attention due to its large magnetoresistance and pressure-induced superconductivity. In this work, we investigate the thermal conductivity (κ) of monolayer WTe2 by performing first-principles calculations, and find strong anisotropic κ with predicted room-temperature values of 9 and 20 W m-1 K-1 along two principal lattice directions, respectively. Such strong anisotropy suggests the importance of orientation when engineering thermal-related applications based on WTe2. The anisotropy of κ is attributed to the in-plane linear acoustic phonon branches, while the out-of-plane quadratic acoustic phonon branch is almost isotropic. The size dependence of κ shows that the size effect can persists up to 10 μm, and the anisotropy decreases with decreasing sample size due to the suppression of low-frequency anisotropic phonons by boundary scattering.
Controller Design of Complex System Based on Nonlinear Strength
Directory of Open Access Journals (Sweden)
Rongjun Mu
2015-01-01
Full Text Available This paper presents a new idea of controller design for complex systems. The nonlinearity index method was first developed for error propagation of nonlinear system. The nonlinearity indices access the boundary between the strong and the weak nonlinearities of the system model. The algorithm of nonlinearity index according to engineering application is first proposed in this paper. Applying this method on nonlinear systems is an effective way to measure the nonlinear strength of dynamics model over the full flight envelope. The nonlinearity indices access the boundary between the strong and the weak nonlinearities of system model. According to the different nonlinear strength of dynamical model, the control system is designed. The simulation time of dynamical complex system is selected by the maximum value of dynamic nonlinearity indices. Take a missile as example; dynamical system and control characteristic of missile are simulated. The simulation results show that the method is correct and appropriate.
Effect of anisotropy on small magnetic clusters
Hucht, Alfred; Sil, Shreekantha; Entel, Peter; 10.1103/PhysRevB.84.104438
2012-01-01
The effect of dipolar interaction and local uniaxial anisotropy on the magnetic response of small spin clusters where spins are located on the vertices of icosahedron, cuboctahedron, tetrahedron and square geometry have been investigated. We consider the ferromagnetic and antiferromagnetic spin-1/2 and spin-1 Heisenberg model with uniaxial anisotropy and dipolar interaction and apply numerical exact diagonalization technique in order to study the influence of frustration and anisotropy on the ground state properties of the spin-clusters. The ground state magnetization, spin-spin correlation and several thermodynamic quantities such as entropy and specific heat are calculated as a function of temperature and magnetic field.
INTERPRETING MAGNETIC VARIANCE ANISOTROPY MEASUREMENTS IN THE SOLAR WIND
Energy Technology Data Exchange (ETDEWEB)
TenBarge, J. M.; Klein, K. G.; Howes, G. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA (United States); Podesta, J. J., E-mail: jason-tenbarge@uiowa.edu [Space Science Institute, Boulder, CO (United States)
2012-07-10
The magnetic variance anisotropy (A{sub m}) of the solar wind has been used widely as a method to identify the nature of solar wind turbulent fluctuations; however, a thorough discussion of the meaning and interpretation of the A{sub m} has not appeared in the literature. This paper explores the implications and limitations of using the A{sub m} as a method for constraining the solar wind fluctuation mode composition and presents a more informative method for interpreting spacecraft data. The paper also compares predictions of the A{sub m} from linear theory to nonlinear turbulence simulations and solar wind measurements. In both cases, linear theory compares well and suggests that the solar wind for the interval studied is dominantly Alfvenic in the inertial and dissipation ranges to scales of k{rho}{sub i} {approx_equal} 5.
Ghosh, Bahniman; Pramanik, Tanmoy; Dey, Rik; Roy, Urmimala; Register, Leonard; Banerjee, Sanjay
2015-03-01
We propose and demonstrate, through simulation, an ultra low energy memory device on a topological insulator thin film. The device consists of a thin layer of Fe deposited on the surface of a topological insulator, Bi2Se3. The top surface of Fe is covered with MgO so that the ferromagnetic layer has perpendicular anisotropy. Current is passed on the surface of the topological insulator which switches the magnetization of the Fe ferromagnet through strong exchange interaction, between electrons contributing to the surface current on the Bi2Se3 and the d electrons in the ferromagnet, and spin transfer torque due to shunting of current through the ferromagnet. Voltage controlled magnetic anisotropy enables ultra low energy switching. Our micromagnetic simulations, predict switching time of the order of 2.4 ns and switching energy of the order of 0.16 fJ for a ferromagnetic bit with thermal stability of 90 kBT. The proposed structure combines the advantages of both large spin torque from topological insulators and those of perpendicular anisotropy materials. This work is supported by NRI SWAN and NSF NASCENT Center.
Ferrimagnetic Properties of Bond Dilution Mixed Blume-Capel Model with Random Single-Ion Anisotropy
Institute of Scientific and Technical Information of China (English)
LIU Lei; YAN Shi-Lei
2005-01-01
We study the ferrimagnetic properties of spin 1/2 and spin-1 systems by means of the effective field theory.The system is considered in the framework of bond dilution mixed Blume-Capel model (BCM) with random single-ion anisotropy. The investigation of phase diagrams and magnetization curves indicates the existence of induced magnetic ordering and single or multi-compensation points. Special emphasis is placed on the influence of bond dilution and random single-ion anisotropy on normal or induced magnetic ordering states and single or multi-compensation points.Normal magnetic ordering states take on new phase diagrams with increasing randomness (bond and anisotropy), while anisotropy induced magnetic ordering states are always occurrence no matter whether concentration of anisotropy is large or small. Existence and disappearance of compensation points rely strongly on bond dilution and random single-ion anisotropy.Some results have not been revealed in Previous papers and predicted by Néel theory of ferrimagnetism.
Yang, Hongxin; Vu, Anh Duc; Hallal, Ali; Rougemaille, Nicolas; Coraux, Johann; Chen, Gong; Schmid, Andreas K; Chshiev, Mairbek
2016-01-13
We report strongly enhanced perpendicular magnetic anisotropy (PMA) of Co films by graphene coating from both first-principles and experiments. Our calculations show that graphene can dramatically boost the surface anisotropy of Co films up to twice the value of its pristine counterpart and can extend the out-of-plane effective anisotropy up to unprecedented thickness of 25 Å. These findings are supported by our experiments on graphene coating on Co films grown on Ir substrate. Furthermore, we report layer-resolved and orbital-hybridization-resolved anisotropy analysis, which help understanding of the physical mechanisms of PMA and more practically can help design structures with giant PMA. As an example, we propose superexchange stabilized Co-graphene heterostructures with a robust constant effective PMA and linearly increasing interfacial anisotropy as a function of film thickness. These findings point toward possibilities to engineer graphene/ferromagnetic metal heterostructures with giant magnetic anisotropy more than 20-times larger compared to conventional multilayers, which constitutes a hallmark for future graphene and traditional spintronic technologies.
Constraints on the source of ultra-high energy cosmic rays using anisotropy vs chemical composition
Liu, Ruo-Yu; Lemoine, Martin; Wang, Xiang-Yu; Waxman, Eli
2013-01-01
The joint analysis of anisotropy signals and chemical composition of ultra-high energy cosmic rays offers strong potential for shedding light on the sources of these particles. Following up on an earlier idea, this paper studies the anisotropies produced by protons of energy >E/Z, assuming that anisotropies at energy >E have been produced by nuclei of charge Z, which share the same magnetic rigidity. We calculate the number of secondary protons produced through photodisintegration of the primary heavy nuclei. Making the extreme assumption that the source does not inject any proton, we find that the source(s) responsible for anisotropies such as reported by the Pierre Auger Observatory should lie closer than ~20-30, 80-100 and 180-200 Mpc if the anisotropy signal is mainly composed of oxygen, silicon and iron nuclei respectively. A violation of this constraint would otherwise result in the secondary protons forming a more significant anisotropy signal at lower energies. Even if the source were located closer t...
Limits on the ion temperature anisotropy in the turbulent intracluster medium
Santos-Lima, R.; Yan, H.; de Gouveia Dal Pino, E. M.; Lazarian, A.
2016-08-01
Turbulence in the weakly collisional intracluster medium (ICM) of galaxies is able to generate strong thermal velocity anisotropies in the ions (with respect to the local magnetic field direction), if the magnetic moment of the particles is conserved in the absence of Coulomb collisions. In this scenario, the anisotropic pressure magnetohydrodynamic (AMHD) turbulence shows a very different statistical behaviour from the standard MHD one and is unable to amplify seed magnetic fields. This is in contrast to previous cosmological MHD simulations that are successful in explaining the observed magnetic fields in the ICM. On the other hand, temperature anisotropies can also drive plasma instabilities that can relax the anisotropy. This work aims to compare the relaxation rate with the growth rate of the anisotropies driven by the turbulence. We employ quasi-linear theory to estimate the ion scattering rate resulting from the parallel firehose, mirror and ion-cyclotron instabilities, for a set of plasma parameters resulting from AMHD simulations of the turbulent ICM. We show that the ICM turbulence can sustain only anisotropy levels very close to the instability thresholds. We argue that the AMHD model that bounds the anisotropies at the marginal stability levels can describe the Alfvénic turbulence cascade in the ICM.
Yang, Hongxin; Vu, Anh Duc; Hallal, Ali; Rougemaille, Nicolas; Coraux, Johann; Chen, Gong; Schmid, Andreas K.; Chshiev, Mairbek
2016-01-01
We report strongly enhanced perpendicular magnetic anisotropy (PMA) of Co films by graphene coating from both first-principles and experiments. Our calculations show that graphene can dramatically boost the surface anisotropy of Co films up to twice the value of its pristine counterpart and can extend the out-of-plane effective anisotropy up to unprecedented thickness of 25~\\AA. These findings are supported by our experiments on graphene coating on Co films grown on Ir substrate. Furthermore, we report layer-resolved and orbital-hybridization-resolved anisotropy analysis which help understanding the physical mechanisms of PMA and more practically can help design structures with giant PMA. As an example, we propose super-exchange stabilized Co-graphene heterostructures with a robust out-of-plane constant effective PMA and linearly increasing interfacial anisotropy as a function of film thickness. These findings point towards possibilities to engineer graphene/ferromagnetic metal heterostructures with giant magnetic anisotropy more than 20 times larger compared to conventional multilayers, which constitutes a hallmark for future graphene and traditional spintronic technologies.
A joint inversion for shear velocity and anisotropy: the Woodlark Rift, Papua New Guinea
Eilon, Zachary; Abers, Geoffrey A.; Gaherty, James B.
2016-08-01
Trade-offs between velocity and anisotropy heterogeneity complicate the interpretation of differential traveltime data and have the potential to bias isotropic tomographic models. By constructing a simple parametrisation to describe an elastic tensor with hexagonal symmetry, we find analytic solutions to the Christoffel equations in terms of fast and slow horizontal velocities that allow us to simultaneously invert differential traveltime data and splitting data from teleseismic S arrivals to recover 3-D velocity and anisotropy structure. This technique provides a constraint on the depth-extent of shallow anisotropy, otherwise absent from interpretations based on SKS splitting alone. This approach is well suited to the young Woodlark Rift, where previous studies have found strong velocity variation and substantial SKS splitting in a continental rift with relatively simple geometry. This study images a low-velocity rift axis with ≤4 per cent spreading-parallel anisotropy at 50-100 km depth that separates regions of pre-existing lithospheric fabric, indicating the synchronous development of extensional crystallographic preferred orientation and lithospheric thinning. A high-velocity slab fragment north of the rift axis is associated with strike-parallel anisotropic fast axes, similar to that seen in the shallow mantle of some subduction zones. In addition to the insights provided by the anisotropy structure, the improvement in fit to the differential traveltime data demonstrates the merit to a joint inversion that accounts for anisotropy.
First-principles characterisation of the pressure-dependent elastic anisotropy of SnO2 polymorphs
Das, Pratik Kumar; Chowdhury, Anjan; Mandal, Nibir; Arya, A.
2016-06-01
Using DFT calculations, this study investigates the pressure-dependent variations of elastic anisotropy in the following SnO2 phases: rutile-type (tetragonal; P42/mnm), CaCl2-type (orthorhombic; Pnnm)-, α-PbO2-type (orthorhombic; Pbcn)- and fluorite-type (cubic; Fm-3m). Experimentally, these polymorphs undergo sequential structural transitions from rutile-type → CaCl2-type → α-PbO2-type → fluorite-type with increasing pressure at 11.35, 14.69 and 58.22 GPa, respectively. We estimate the shear anisotropy (A1 and A3) on {1 0 0} and {0 0 1} crystallographic planes of the tetragonal phase and (A1, A2 and A3) on {1 0 0}, {0 1 0} and {0 0 1} crystallographic planes of the orthorhombic phases. The rutile-type phase shows strongest shear anisotropy on the {0 0 1} planes (A2 > 4.8), and the degree of anisotropy increases nonlinearly with pressure. In contrast, the anisotropy is almost absent on the {1 0 0} planes (ie A1 1) irrespective of the pressure. The CaCl2-type phase exhibits similar shear anisotropy behaviour preferentially on {0 0 1} (A3 > 5), while A1 and A2 remain close to 1. The α-PbO2-type phase shows strikingly different elastic anisotropy characterised by a reversal in anisotropy (A3 > 1 to < 1) with increasing pressure at a threshold value of 38 GPa. We provide electronic density of states and atomic configuration to account for this pressure-dependent reversal in shear anisotropy. Our study also analyses the directional Young's moduli for the tetragonal and orthorhombic phases as a function of pressure. Finally, we estimate the band gaps of these four SnO2 phases as a function of pressure which are in agreement with the previous results.
Wiyono, Samsul H.; Nugraha, Andri Dian
2015-04-01
Determining of seismic anisotropy allowed us for understanding the deformation processes that occured in the past and present. In this study, we performed shear wave splitting to characterize seismic anisotropy beneath Sunda-Banda subduction-collision zone. For about 1,610 XKS waveforms from INATEWS-BMKG networks have been analyzed. From its measurements showed that fast polarization direction is consistent with trench-perpendicular orientation but several stations presented different orientation. We also compared between fast polarization direction with absolute plate motion in the no net rotation and hotspot frame. Its result showed that both absolute plate motion frame had strong correlation with fast polarization direction. Strong correlation between the fast polarization direction and the absolute plate motion can be interpreted as the possibility of dominant anisotropy is in the asthenosphere..
Energy Technology Data Exchange (ETDEWEB)
Wiyono, Samsul H., E-mail: samsul.wiyono@bmkg.go.id [Study Program of Earth Sciences, Faculty of Earth Sciences and Technology, Institute of Technology Bandung, Bandung 40132 (Indonesia); Indonesia’s Agency for Meteorology Climatology and Geophysics, Jakarta 10610 (Indonesia); Nugraha, Andri Dian, E-mail: nugraha@gf.itb.ac.id [Indonesia’s Agency for Meteorology Climatology and Geophysics, Jakarta 10610 (Indonesia); Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institute of Technology Bandung, Bandung 40132, Indonesia, Phone: +62-22 2534137 (Indonesia)
2015-04-24
Determining of seismic anisotropy allowed us for understanding the deformation processes that occured in the past and present. In this study, we performed shear wave splitting to characterize seismic anisotropy beneath Sunda-Banda subduction-collision zone. For about 1,610 XKS waveforms from INATEWS-BMKG networks have been analyzed. From its measurements showed that fast polarization direction is consistent with trench-perpendicular orientation but several stations presented different orientation. We also compared between fast polarization direction with absolute plate motion in the no net rotation and hotspot frame. Its result showed that both absolute plate motion frame had strong correlation with fast polarization direction. Strong correlation between the fast polarization direction and the absolute plate motion can be interpreted as the possibility of dominant anisotropy is in the asthenosphere.
Interpretation of the Global Anisotropy in the Radio Polarizations of Cosmologically Distant Sources
Indian Academy of Sciences (India)
Pankaj Jain; S. Sarala
2006-12-01
We present a detailed statistical study of the observed anisotropy in radio polarizations from distant extragalactic objects. This anisotropy was earlier found by Birch (1982) and reconfirmed by Jain and Ralston (1999) in a larger data set. A very strong signal was seen after imposing the cut $|RM-\\overline{RM}| \\gt 6$ rad/m2, where RM is the rotation measure and $\\overline{RM}$ its mean value. In this paper, we show that there are several indications that this anisotropy cannot be attributed to bias in the data. We also find that a generalized statistic shows a very strong signal in the entire data without imposing the RM dependent cut. Finally we argue that an anisotropic background pseudoscalar field can explain the observations.
Controllability of nonlinear systems.
Sussmann, H. J.; Jurdjevic, V.
1972-01-01
Discussion of the controllability of nonlinear systems described by the equation dx/dt - F(x,u). Concepts formulated by Chow (1939) and Lobry (1970) are applied to establish criteria for F and its derivatives to obtain qualitative information on sets which can be obtained from x which denotes a variable of state in an arbitrary, real, analytical manifold. It is shown that controllability implies strong accessibility for a large class of manifolds including Euclidean spaces.-
The Kerr nonlinearity of the beta-barium borate crystal
DEFF Research Database (Denmark)
Bache, Morten; Guo, Hairun; Zhou, Binbin
2013-01-01
A popular crystal for ultrafast cascading experiments is beta-barium-borate (β-BaB2O4, BBO). It has a decent quadratic nonlinear coefficient, and because the crystal is anisotropie it can be birefringence phase-matched for type I (oo → e) second-harmonic generation (SHG). For femtosecond...
Nonlinear Oscillators in Space Physics
Lester,Daniel; Thronson, Harley
2011-01-01
We discuss dynamical systems that produce an oscillation without an external time dependent source. Numerical results are presented for nonlinear oscillators in the Em1h's atmosphere, foremost the quasi-biennial oscillation (QBOl. These fluid dynamical oscillators, like the solar dynamo, have in common that one of the variables in a governing equation is strongly nonlinear and that the nonlinearity, to first order, has particular form. of 3rd or odd power. It is shown that this form of nonlinearity can produce the fundamental li'equency of the internal oscillation. which has a period that is favored by the dynamical condition of the fluid. The fundamental frequency maintains the oscillation, with no energy input to the system at that particular frequency. Nonlinearities of 2nd or even power could not maintain the oscillation.
Rosin, M S; Rincon, F; Cowley, S C
2010-01-01
Plasmas have a natural tendency to develop pressure anisotropies with respect to the local direction of the magnetic field. These anisotropies trigger plasma instabilities at scales just above the ion Larmor radius with growth rates of a fraction of the ion cyclotron frequency - much faster than either the global dynamics or local turbulence. The instabilities can dramatically modify the macroscopic dynamics of the plasma. Nonlinear evolution of these instabilities is expected to drive pressure anisotropies towards marginal stability values, controlled by the plasma beta. This nonlinear evolution is worked out in an ab initio kinetic calculation for the simplest analytically tractable example - the parallel firehose instability in a high-beta plasma. A closed nonlinear equation for the firehose turbulence is derived and solved. In the nonlinear regime, the instability leads to secular (~t) growth of magnetic fluctuations. The fluctuations develop a k^{-3} spectrum, extending from scales somewhat larger than r...
In, Visarath; Longhini, Patrick; Kho, Andy; Neff, Joseph D.; Leung, Daniel; Liu, Norman; Meadows, Brian K.; Gordon, Frank; Bulsara, Adi R.; Palacios, Antonio
2012-12-01
The nonlinear channelizer is an integrated circuit made up of large parallel arrays of analog nonlinear oscillators, which, collectively, serve as a broad-spectrum analyzer with the ability to receive complex signals containing multiple frequencies and instantaneously lock-on or respond to a received signal in a few oscillation cycles. The concept is based on the generation of internal oscillations in coupled nonlinear systems that do not normally oscillate in the absence of coupling. In particular, the system consists of unidirectionally coupled bistable nonlinear elements, where the frequency and other dynamical characteristics of the emergent oscillations depend on the system's internal parameters and the received signal. These properties and characteristics are being employed to develop a system capable of locking onto any arbitrary input radio frequency signal. The system is efficient by eliminating the need for high-speed, high-accuracy analog-to-digital converters, and compact by making use of nonlinear coupled systems to act as a channelizer (frequency binning and channeling), a low noise amplifier, and a frequency down-converter in a single step which, in turn, will reduce the size, weight, power, and cost of the entire communication system. This paper covers the theory, numerical simulations, and some engineering details that validate the concept at the frequency band of 1-4 GHz.
Anisotropy and Corotation of Galactic Cosmic Rays
Amenomori, M; Bi, X J; Chen, D; Cui, S W; Danzengluobu; Ding, L K; Ding, X H; Feng Cun Feng; Zhaoyang Feng; Feng, Z Y; Gao, X Y; Geng, Q X; Guo, H W; He, H H; He, M; Hibino, K; Hotta, N; Haibing, H; Hu, H B; Huang, J; Huang, Q; Jia, H Y; Kajino, F; Kasahara, K; Katayose, Y; Kato, C; Kawata, K; Labaciren; Le, G M; Li, A F; Li, J Y; Lou, Y Q; Lü, H; Lu, S L; Meng, X R; Mizutani, K; Mu, J; Munakata, K; Nagai, A; Nanjo, H; Nishizawa, M; Ohnishi, M; Ohta, I; Onuma, H; Ouchi, T; Ozawa, S; Ren, J R; Saitô, T; Saito, T Y; Sakata, M; Sako, T K; Sasaki, T; Shibata, M; Shiomi, A; Shirai, T; Sugimoto, H; Takita, M; Tan, Y H; Tateyama, N; Torii, S; Tsuchiya, H; Udo, S; Wang, B; Wang, H; Wang, X; Wang, Y G; Wu, H R; Xue Liang; Yamamoto, Y; Yan, C T; Yang, X C; Yasue, S; Ye, Z H; Yu, G C; Yuan, A F; Yuda, T; Zhang, H M; Zhang, J L; Zhang, N J; Zhang, X Y; Zhang, Y; Zhaxisangzhu; Zhou, X X
2006-01-01
The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments.
Cellulose and the Control of Growth Anisotropy
Energy Technology Data Exchange (ETDEWEB)
Tobias I. Baskin
2004-04-01
The authors research aims to understand morphogenesis, focusing on growth anisotropy, a process that is crucial to make organs with specific and heritable shapes. For the award, the specific aims were to test hypotheses concerning how growth anisotropy is controlled by cell wall structure, particularly by the synthesis and alignment of cellulose microfibrils, the predominant mechanical element in the cell wall. This research has involved characterizing the basic physiology of anisotropic expansion, including measuring it at high resolution; and second, characterizing the relationship between growth anisotropy, and cellulose microfibrils. Important in this relationship and also to the control of anisotropic expansion are structures just inside the plasma membrane called cortical microtubules, and the research has also investigated their contribution to controlling anisotropy and microfibril alignment. In addition to primary experimental papers, I have also developed improved methods relating to these objectives as well as written relevant reviews. Major accomplishments in each area will now be described.
Elastic anisotropy of Earth's inner core.
Belonoshko, Anatoly B; Skorodumova, Natalia V; Rosengren, Anders; Johansson, Börje
2008-02-08
Earth's solid-iron inner core is elastically anisotropic. Sound waves propagate faster along Earth's spin axis than in the equatorial plane. This anisotropy has previously been explained by a preferred orientation of the iron alloy hexagonal crystals. However, hexagonal iron becomes increasingly isotropic on increasing temperature at pressures of the inner core and is therefore unlikely to cause the anisotropy. An alternative explanation, supported by diamond anvil cell experiments, is that iron adopts a body-centered cubic form in the inner core. We show, by molecular dynamics simulations, that the body-centered cubic iron phase is extremely anisotropic to sound waves despite its high symmetry. Direct simulations of seismic wave propagation reveal an anisotropy of 12%, a value adequate to explain the anisotropy of the inner core.
Magnetic anisotropies of rare-earth compounds
Loewenhaupt, M.; Rotter, M.; Kramp, S.
2000-03-01
There are two kinds of magnetic anisotropy in rare-earth compounds: the single-ion anisotropy caused by the crystal field (CF) and the anisotropy of the two-ion interactions. Both types of anisotropy have to be considered to arrive at a consistent description of the magnetic properties of the orthorhombic intermetallic compound NdCu 2. From the analysis of NdCu 2 we can derive predictions for the type of ordering in other isostructural RCu 2 compounds, that agree well with experimental results: If the magnetic moments point into the crystallographic b-direction, an ordering wave vector of (2/3 0 0) is expected. If the moments are oriented perpendicular to b then the ordering wave vector is (2/3 1 0) .
Microwave Background Anisotropies from Scaling Seed Perturbations
Durrer, R; Durrer, Ruth; Sakellariadou, Mairi
1997-01-01
We study microwave background anisotropies induced by scaling seed perturbations in a universe dominated by cold dark matter. Using a gauge invariant linear perturbation analysis, we solve the perturbation equations on super-horizon scales, for CMB anisotropies triggered by generic gravitational seeds. We find that perturbations induced by seeds -- under very mild restrictions -- are nearly isocurvature. Thus, compensation, which is mainly the consequence of physically sensible initial conditions, is very generic. We then restrict our study to the case of scaling sources, motivated by global scalar fields. We parameterize the energy momentum tensor of the source by ``seed functions'' and calculate the Sachs-Wolfe and acoustic contributions to the CMB anisotropies. We discuss the dependence of the anisotropy spectrum on the parameters of the model considered. Even within the restricted class of models investigated in this work, we find a surprising variety of results for the position and height of the first ac...
Strongly interacting light dark matter
Energy Technology Data Exchange (ETDEWEB)
Bruggisser, Sebastian [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Riva, Francesco; Urbano, Alfredo [CERN, Geneva (Switzerland). Theoretical Physics Dept.
2016-07-15
In the presence of approximate global symmetries that forbid relevant interactions, strongly coupled light Dark Matter (DM) can appear weakly coupled at small-energy and generate a sizable relic abundance. Fundamental principles like unitarity restrict these symmetries to a small class, where the leading interactions are captured by effective operators up to dimension-8. Chiral symmetry, spontaneously broken global symmetries and non-linearly realized supersymmetry are examples of this. Their DM candidates (composite fermions, pseudo-Nambu-Goldstone Bosons and Goldstini) are interesting targets for LHC missing-energy searches.
Strongly Interacting Light Dark Matter
Bruggisser, Sebastian; Urbano, Alfredo
2016-01-01
In the presence of approximate global symmetries that forbid relevant interactions, strongly coupled light Dark Matter (DM) can appear weakly coupled at small energy and generate a sizable relic abundance. Fundamental principles like unitarity restrict these symmetries to a small class, where the leading interactions are captured by effective operators up to dimension-8. Chiral symmetry, spontaneously broken global symmetries and non-linearly realized supersymmetry are examples of this. Their DM candidates (composite fermions, pseudo Nambu-Goldstone Bosons and Goldstini) are interesting targets for LHC missing-energy searches.
Higher-order anisotropies in the Buda-Lund model: Disentangling flow and density field anisotropies
Energy Technology Data Exchange (ETDEWEB)
Loekoes, Sandor [Eoetvoes Lorand University, Budapest (Hungary); Csanad, Mate [Eoetvoes Lorand University, Budapest (Hungary); Stony Brook University, Stony Brook, NY (United States); Tomasik, Boris [Univerzita Mateja Bela, Banska Bystrica (Slovakia); Czech Technical University in Prague, FNSPE, Prague (Czech Republic); Csoergo, Tamas [Wigner RCP, Budapest (Hungary); KRF, Gyoengyoes (Hungary)
2016-10-15
The Buda-Lund hydro model describes an expanding ellipsoidal fireball, and fits the observed elliptic flow and oscillating HBT radii successfully. Due to fluctuations in energy depositions, the fireball shape however fluctuates on an event-by-event basis. The transverse plane asymmetry can be translated into a series of multipole anisotropy coefficients. These anisotropies then result in measurable momentum-space anisotropies, to be measured with respect to their respective symmetry planes. In this paper we detail an extension of the Buda-Lund model to multipole anisotropies and investigate the resulting flow coefficients and oscillations of HBT radii. (orig.)
Lökös, Sándor; Csörgő, Tamás; Tomášik, Boris
2016-01-01
The Buda-Lund hydro model describes an expanding ellipsoidal fireball, and fits the observed elliptic flow and oscillating HBT radii successfully. Due to fluctuations in energy depositions, the fireball shape however fluctuates on an event-by-event basis. The transverse plane asymmetry can be translated into a series of multipole anisotropy coefficients. These anisotropies then result in measurable momentum-space anisotropies, to be measured with respect to their respective symmetry planes. In this paper we detail an extension of the Buda-Lund model to multipole anisotropies and investigate the resulting flow coefficients and oscillations of HBT radii.
X-ray analysis of oxygen-induced perpendicular magnetic anisotropy in Pt/Co/AlO{sub x} trilayers
Energy Technology Data Exchange (ETDEWEB)
Manchon, A. [SPINTEC, URA 2512 CEA/CNRS, CEA/Grenoble, 38054 Grenoble Cedex 9 (France)], E-mail: aurelien.manchon@m4x.org; Pizzini, S.; Vogel, J.; Uhlir, V. [Institut Neel, CNRS/UJF, B.P. 166, 38042 Grenoble Cedex 9 (France); Lombard, L.; Ducruet, C.; Auffret, S.; Rodmacq, B.; Dieny, B. [SPINTEC, URA 2512 CEA/CNRS, CEA/Grenoble, 38054 Grenoble Cedex 9 (France); Hochstrasser, M. [Laboratory for Solid State Physics, ETH Zuerich, 8093 Zuerich (Switzerland); Panaccione, G. [Laboratory TASC, INFM-CNR, Area Science Park, S.S.14, Km 163.5, I-34012, Trieste (Italy)
2008-07-15
X-ray spectroscopy measurements have been performed on a series of Pt/Co/AlO{sub x} trilayers to investigate the role of Co oxidation in the perpendicular magnetic anisotropy of the Co/AlO{sub x} interface. It is observed that high temperature annealing modifies the magnetic properties of the Co layer, inducing an enhancement of the perpendicular magnetic anisotropy. The microscopic structural properties are analyzed via X-ray Absorption Spectroscopy, X-ray Magnetic Circular Dichroism and X-ray Photoelectron Spectroscopy measurements. It is shown that annealing enhances the amount of interfacial oxide, which may be at the origin of a strong perpendicular magnetic anisotropy.
Guan, X. W.; Cheng, X. M.; Wang, S.; Huang, T.; Xue, K. H.; Miao, X. S.
2016-06-01
The impact of the MgO/Fe interface oxidation state on the electric-field-modified magnetic anisotropy in MgO/Fe has been revealed by density functional calculations. It is shown that the influence of the interface oxidation is strong enough to dominate the effect of the electric field on the magnetic anisotropy of MgO/Fe-based films. The magnetoelectric coefficients are calculated to be positive for the ideal and overoxidized MgO/Fe interface, but an abnormal negative value emerges in the underoxidized case. By analyzing the interface states based on density of states and band structures, we demonstrate that the considerably different electronic structures of the three oxidized MgO/Fe interfaces lead to the strong discrepancy in the electric-field modulation of the interfacial magnetic anisotropy. These results are of considerable interest in the area of electric-field-controlled magnetic anisotropy and switching.
Lee, Sangyeop; Choi, Seonghoon; Bac, Seul-Ki; Lee, Hakjoon; Yoo, Taehee; Lee, Sanghoon; Liu, X.; Furdyna, J. K.
2016-10-01
We used the Hall effect and magnetization measurements to investigate the temperature dependence of the magnetic anisotropy of a ferromagnetic semiconductor GaMnAs film grown on a (001) GaAs substrate. The Hall effect was systematically measured by applying an external magnetic field within and normal to the film plane. The switching behavior of the magnetization during the reversal process revealed the coexistence of in-plane and out-of-plane magnetic anisotropies in the film. However, these two types of magnetic anisotropies strongly depended on the temperature. Specifically, the out-of-plane anisotropy was dominant in the low-temperature region (i.e., 3-10 K), whereas the in-plane anisotropy became dominant in the temperature region higher than 15 K. This temperature dependent change in the magnetic anisotropy was further confirmed using direct magnetization measurements.
Nozaki, Takayuki; Kozioł-Rachwał, Anna; Skowroński, Witold; Zayets, Vadym; Shiota, Yoichi; Tamaru, Shingo; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji; Suzuki, Yoshishige
2016-04-01
We study the voltage control of perpendicular magnetic anisotropy in an ultrathin Fe layer sandwiched between the Cr buffer and MgO tunneling barrier layers. A high-interface magnetic anisotropy energy of 2.1 mJ /m2 is achieved in the Cr/ultrathin Fe /MgO structure. A large voltage-induced perpendicular magnetic anisotropy change is observed under the negative-bias voltage applications for the case of the Fe layer thinner than 0.6 nm. The amplitude of the voltage-induced anisotropy energy change exhibits a strong Fe-thickness dependence and it reaches as high as 290 fJ /Vm . The observed high values of the surface anisotropy and voltage-induced anisotropy energy change demonstrate the feasibility of voltage-driven spintronic devices.
Energy Technology Data Exchange (ETDEWEB)
Turchetti, G. (Bologna Univ. (Italy). Dipt. di Fisica)
1989-01-01
Research in nonlinear dynamics is rapidly expanding and its range of applications is extending beyond the traditional areas of science where it was first developed. Indeed while linear analysis and modelling, which has been very successful in mathematical physics and engineering, has become a mature science, many elementary phenomena of intrinsic nonlinear nature were recently experimentally detected and investigated, suggesting new theoretical work. Complex systems, as turbulent fluids, were known to be governed by intrinsically nonlinear laws since a long time ago, but received purely phenomenological descriptions. The pioneering works of Boltzmann and Poincare, probably because of their intrinsic difficulty, did not have a revolutionary impact at their time; it is only very recently that their message is reaching a significant number of mathematicians and physicists. Certainly the development of computers and computer graphics played an important role in developing geometric intuition of complex phenomena through simple numerical experiments, while a new mathematical framework to understand them was being developed.
Confinining properties of QCD in strong magnetic backgrounds
Directory of Open Access Journals (Sweden)
Bonati Claudio
2017-01-01
Full Text Available Strong magnetic backgrounds are known to modify QCD properties at a nonperturbative level. We discuss recent lattice results, obtained for Nf = 2 + 1 QCD with physical quark masses, concerning in particular the modifications and the anisotropies induced at the level of the static quark-antiquark potential, both at zero and finite temperature.
Theory of Spin Waves in Strongly Anisotropic Magnets
DEFF Research Database (Denmark)
Lindgård, Per-Anker; Cooke, J. F.
1976-01-01
A new infinite-order perturbation approach to the theory of spin waves in strongly anisotropic magnets is introduced. The system is transformed into one with effective two-ion anisotropy and considerably reduced ground-state corrections. A general expression for the spin-wave energy, valid to any...
The perpendicular magnetic anisotropy of CoPt/Au multilayer films
Energy Technology Data Exchange (ETDEWEB)
Yokota, T. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Gao, L. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Zhang, R. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Nicholl, L. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Yan, M.L. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Sellmyer, D.J. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Liou, S.H. [Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States)]. E-mail: sliou@unl.edu
2005-02-01
We have studied the magnetic properties of Au (2 nm)/Co{sub 50}Pt{sub 50} (3 nm)/Au (2 nm) multilayer films prepared on amorphous Al{sub 2}O{sub 3}/Si and (0 0 1) MgO substrates. The as-deposited films on both substrates are magnetically soft with an FCC structure and exhibit a perpendicular anisotropy. After annealing at 500 deg. C, the sample on the Al{sub 2}O{sub 3}/Si substrate has become magnetically isotropic but the sample on the MgO substrate still has perpendicular anisotropy with FCT structure. This film deposited on the MgO substrate did not show a strong perpendicular anisotropy due to the diffusion of the Au and the (1 1 1) nucleation of initial Au layer. We can obtain a perpendicular anisotropy in the multilayer films without an initial Au layer on a (0 0 1) MgO substrate. After annealing at 400 deg. C, these films have L1{sub 0} phase with (0 0 1) texture and strong perpendicular anisotropy.
Dissipative Nonlinear Dynamics in Holography
Basu, Pallab
2013-01-01
We look at the response of a nonlinearly coupled scalar field in an asymptotically AdS black brane geometry and find a behaviour very similar to that of known dissipative nonlinear systems like the chaotic pendulum. Transition to chaos proceeds through a series of period-doubling bifurcations. The presence of dissipation, crucial to this behaviour, arises naturally in a black hole background from the ingoing conditions imposed at the horizon. AdS/CFT translates our solution to a chaotic response of the operator dual to the scalar field. Our setup can also be used to study quench-like behaviour in strongly coupled nonlinear systems.
DEFF Research Database (Denmark)
Manoonpong, Poramate; Petersen, Dennis; Kovalev, Alexander
2016-01-01
stability. It shows high frictional anisotropy due to an array of sloped denticles. The orientation of the denticles to the underlying collagenous material also strongly influences their mechanical interlocking with the substrate. This study not only opens up a new way of achieving energy-efficient legged...
Nonlinear field space cosmology
Mielczarek, Jakub; Trześniewski, Tomasz
2017-08-01
We consider the FRW cosmological model in which the matter content of the Universe (playing the role of an inflaton or quintessence) is given by a novel generalization of the massive scalar field. The latter is a scalar version of the recently introduced nonlinear field space theory, where the physical phase space of a given field is assumed to be compactified at large energies. For our analysis, we choose the simple case of a field with the spherical phase space and endow it with the generalized Hamiltonian analogous to the XXZ Heisenberg model, normally describing a system of spins in condensed matter physics. Subsequently, we study both the homogenous cosmological sector and linear perturbations of such a test field. In the homogenous sector, we find that nonlinearity of the field phase space is becoming relevant for large volumes of the Universe and can lead to a recollapse, and possibly also at very high energies, leading to the phase of a bounce. Quantization of the field is performed in the limit where the nontrivial nature of its phase space can be neglected, while there is a nonvanishing contribution from the Lorentz symmetry breaking term of the Hamiltonian. As a result, in the leading order of the XXZ anisotropy parameter, we find that the inflationary spectral index remains unmodified with respect to the standard case but the total amplitude of perturbations is subject to a correction. The Bunch-Davies vacuum state also becomes appropriately corrected. The proposed new approach is bringing cosmology and condensed matter physics closer together, which may turn out to be beneficial for both disciplines.
Seider, Warren D.; Ungar, Lyle H.
1987-01-01
Describes a course in nonlinear mathematics courses offered at the University of Pennsylvania which provides an opportunity for students to examine the complex solution spaces that chemical engineers encounter. Topics include modeling many chemical processes, especially those involving reaction and diffusion, auto catalytic reactions, phase…
Beik Mohammadi, Jamileh; Jones, Joshua Michael; Paul, Soumalya; Khodadadi, Behrouz; Mewes, Claudia K. A.; Mewes, Tim; Kaiser, Christian
2017-02-01
The magnetization dynamics of exchange-biased IrMn/CoFe bilayers have been investigated using broadband and in-plane angle-dependent ferromagnetic resonance spectroscopy. The interface energy of the exchange bias effect in these bilayers exceeds values previously reported for metallic antiferromagnets. A strong perpendicular magnetic anisotropy and a small in-plane uniaxial anisotropy are also observed in these films. The magnetization relaxation of the bilayers has a strong unidirectional contribution, which is in part caused by two-magnon scattering. However, a detailed analysis of in-plane angle- and thickness-dependent linewidth data strongly suggests the presence of a previously undescribed unidirectional relaxation mechanism.
Mamatsashvili, George; Dong, Siwei; Khujadze, George; Chagelishvili, George; Jiménez, Javier; Foysi, Holger
2016-04-01
We performed direct numerical simulations of homogeneous shear turbulence to study the mechanism of the self-sustenance of subcritical turbulence in spectrally stable (constant) shear flows. For this purpose, we analyzed the turbulence dynamics in Fourier/wavenumber/spectral space based on the simulation data for the domain aspect ratio 1 : 1 : 1. Specifically, we examined the interplay of linear transient growth of Fourier harmonics and nonlinear processes. The transient growth of harmonics is strongly anisotropic in spectral space. This, in turn, leads to anisotropy of nonlinear processes in spectral space and, as a result, the main nonlinear process appears to be not a direct/inverse, but rather a transverse/angular redistribution of harmonics in Fourier space referred to as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by the interplay of the linear transient, or nonmodal growth and the transverse cascade. This course of events reliably exemplifies the wellknown bypass scenario of subcritical turbulence in spectrally stable shear flows. These processes mainly operate at large length scales, comparable to the box size. Consequently, the central, small wavenumber area of Fourier space (the size of which is determined below) is crucial in the self-sustenance and is labeled the vital area. Outside the vital area, the transient growth and the transverse cascade are of secondary importance - Fourier harmonics are transferred to dissipative scales by the nonlinear direct cascade. The number of harmonics actively participating in the self-sustaining process (i.e., the harmonics whose energies grow more than 10% of the maximum spectral energy at least once during evolution) is quite large - it is equal to 36 for the considered box aspect ratio - and obviously cannot be described by low-order models.
Mantle wedge dynamics from seismic anisotropy (Invited)
Long, M. D.; Wirth, E. A.
2013-12-01
The mantle wedge above subducting slabs plays a critical role in many of the physical processes associated with subduction, including water transport into the upper mantle and the generation and transport of melts. Our understanding of mantle wedge dynamics is incomplete; in particular, the mantle flow field above subducting slabs remains poorly understood. Because seismic anisotropy is a consequence of deformation, observations of anisotropy (such as shear wave splitting and P-to-SH converted waves) can constrain the geometry of the wedge flow field. Additionally, because the presence of water (either in nominally anhydrous minerals or as hydrous phases) can have a large effect on anisotropic structure, a detailed understanding of mantle wedge anisotropy can help to constrain processes related to water cycling in subduction systems. We present a global, synoptic view of anisotropy observations in subduction zone mantle wedges, compiled from a large number of individual studies, with the goal of understanding the first-order controls on wedge anisotropy and flow patterns. This compilation allows us to explicitly test the predictions made by many different conceptual models for wedge anisotropy, as well as to explore the relationships between observed anisotropy parameters and other parameters that describe subduction. We find that no simple model can explain all of the trends observed in the global data set. Mantle wedge flow is likely controlled by a combination of downdip motion of the slab, trench migration, ambient mantle flow, small-scale convection, proximity to slab edges, and slab morphology, with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology. There is also a likely contribution from B-type olivine and/or serpentinite fabric in many subduction zones, governed by the local thermal structure and volatile distribution.
Topological nature of nonlinear optical effects in solids
Morimoto, Takahiro; Nagaosa, Naoto
2015-01-01
There are a variety of nonlinear optical effects including higher harmonic generations, photovoltaic effects, and nonlinear Kerr rotations. They are realized by the strong light irradiation to materials that results in nonlinear polarizations in the electric field. These are of great importance in studying the physics of excited states of the system as well as for applications to optical devices and solar cells. Nonlinear properties of materials are usually described by the nonlinear suscepti...
Structure and magnetic properties of nanocrystalline ferromagnets (Ⅰ)--Effective anisotropy
Institute of Scientific and Technical Information of China (English)
刘涛; 徐祖雄; 赵钟涛; 马如璋; 胡天斗; 谢亚宁; 郭应焕
1997-01-01
The role of effective anisotropy in nanocrystalline ferromagnets is investigated. These alloys are prepared by annealing amorphous ribbons and have excellent soft magnetic properties. A two-phase model is established considering the role of the mtergranular amorphous phase. The results indicate a strong dependence of effective anisotropy on the structure and magnetic parameters of the amorphous phase as well as on the size of a grains. In view of the new model, the magnetic hardening beyond the optimally annealing temperature seems to be ascribed to the de-terioration in magnetic properties of interfacial amorphous phase.
1989-01-01
aublattice anisotropy. 1. Introduction The compound Nd2Fe14B is the basic material for the production of high quality Permanent magniets [1, 21. It...the in-plane anisotropy is in disagreement with the observed different magnetiza- tion curves for Nd2Fe14B in the [1001 and [1101 directions [101... Nd2Fe14B based permanent magnets so far. The grain size of the magnets also strongly der ds on the processing technique. The electron micrographs of Fig
Macroscopic anisotropy and symmetry breaking in the pyrochlore antiferromagnet Gd2Ti2O7
Hassan, A. K.; Lévy, L. P.; Darie, C.; Strobel, P.
2003-06-01
In the Heisenberg antiferromagnet Gd2Ti2O7, the exchange interactions are geometrically frustrated by the pyrochlore lattice structure. This ESR study reveals a strong temperature dependent anisotropy with respect to a [111] body diagonal below a temperature TA=80 K, despite the spin only nature of the Gd3+ ion. Anisotropy and symmetry breaking can nevertheless appear through the superexchange interaction. In the presence of anisotropic exchanges, short range planar correlations restricted to specific Kagomé planes are sufficient to explain the two ESR modes studied in this work.
Gerhardt, Theo; Drews, André; Meier, Guido
2012-01-18
We investigate switching and field-driven domain wall motion in nanowires with perpendicular magnetic anisotropy comprising local modifications of the material parameters. Intentional nucleation and pinning sites with various geometries inside the nanowires are realized via a local reduction of the anisotropy constant. Micromagnetic simulations and analytical calculations are employed to determine the switching fields and to characterize the pinning potentials and the depinning fields. Nucleation sites in the simulations cause a significant reduction of the switching field and are in excellent agreement with analytical calculations. Pinning potentials and depinning fields caused by the pinning sites strongly depend on their shapes and are well explained by analytical calculations.
Engineering spin-orbit torque in Co/Pt multilayers with perpendicular magnetic anisotropy
Energy Technology Data Exchange (ETDEWEB)
Huang, Kuo-Feng; Wang, Ding-Shuo; Lai, Chih-Huang, E-mail: chlai@mx.nthu.edu.tw [Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Lin, Hsiu-Hau [Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China)
2015-12-07
To address thermal stability issues for spintronic devices with a reduced size, we investigate spin-orbit torque in Co/Pt multilayers with strong perpendicular magnetic anisotropy. Note that the spin-orbit torque arises from the global imbalance of the spin currents from the top and bottom interfaces for each Co layer. By inserting Ta or Cu layers to strengthen the top-down asymmetry, the spin-orbit torque efficiency can be greatly modified without compromised perpendicular magnetic anisotropy. Above all, the efficiency builds up as the number of layers increases, realizing robust thermal stability and high spin-orbit-torque efficiency simultaneously in the multilayers structure.
Engineering spin-orbit torque in Co/Pt multilayers with perpendicular magnetic anisotropy
Huang, Kuo-Feng; Wang, Ding-Shuo; Lin, Hsiu-Hau; Lai, Chih-Huang
2015-12-01
To address thermal stability issues for spintronic devices with a reduced size, we investigate spin-orbit torque in Co/Pt multilayers with strong perpendicular magnetic anisotropy. Note that the spin-orbit torque arises from the global imbalance of the spin currents from the top and bottom interfaces for each Co layer. By inserting Ta or Cu layers to strengthen the top-down asymmetry, the spin-orbit torque efficiency can be greatly modified without compromised perpendicular magnetic anisotropy. Above all, the efficiency builds up as the number of layers increases, realizing robust thermal stability and high spin-orbit-torque efficiency simultaneously in the multilayers structure.
Moon, Kyoung-Woong; Lee, Jae-Chul; Choe, Sug-Bong; Shin, Kyung-Ho
2009-11-01
A magnetometric technique for detecting the magnetic anisotropy field of ferromagnetic films is described. The technique is based on the extraordinary Hall voltage measurement with rotating the film under an external magnetic field. By analyzing the angle-dependent Hall voltage based on the Stoner-Wohlfarth theory, the magnetic anisotropy field is uniquely determined. The present technique is pertinent especially for ultrathin films with strong intrinsic signal, in contrast to the conventional magnetometric techniques of which the signal is in proportion to the sample volume and geometry.
Wang, Jing; Chen, Junzhu; Liu, Jinlong; Wang, Zhuo; Li, Yiheng; Guo, Qi; Hu, Wei; Xuan, Li
2015-01-01
We investigate theoretically and experimentally the optical beam propagation in the nematic liquid crystal with negative dielectric anisotropy, which is aligned homeotropically in a $80\\mu m$-thickness planar cell in the presence of an externally voltage. It is predicted that the nonlocal nonlinearity of liquid crystal undergo an oscillatory response function with a negative nonlinear refractive index coefficient. We found that the oscillatory nonlocal nonlinearity can support stable bright solitons, which are observed in experiment. We also found that abnormal modulation instability occurs with infinity gain coefficient at a fixed spatial frequency, which is no depend on the beam intensity. We observed the modulation instability in the liquid crystal at a very low intensity ($0.26W/cm^2$), and the maximum gain frequency were found kept unchange when beam power changes over 2-3 orders of magnitude.
Azimuthal anisotropies as stringent test for nuclear transport models
Crochet, P.; Rami, F.; Donà, R.; Coffin, J. P.; Fintz, P.; Guillaume, G.; Jundt, F.; Kuhn, C.; Roy, C.; de Schauenburg, B.; Tizniti, L.; Wagner, P.; Alard, J. P.; Andronic, A.; Basrak, Z.; Bastid, N.; Belyaev, I.; Bendarag, A.; Berek, G.; Best, D.; Biegansky, J.; Buta, A.; Čaplar, R.; Cindro, N.; Dupieux, P.; Dželalija, M.; Fan, Z. G.; Fodor, Z.; Fraysse, L.; Freifelder, R. P.; Gobbi, A.; Herrmann, N.; Hildenbrand, K. D.; Hong, B.; Jeong, S. C.; Kecskemeti, J.; Kirejczyk, M.; Koncz, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Manko, V.; Moisa, D.; Mösner, J.; Neubert, W.; Pelte, D.; Petrovici, M.; Pinkenburg, C.; Reisdorf, W.; Ritman, J. L.; Sadchikov, A. G.; Schüll, D.; Seres, Z.; Sikora, B.; Simion, V.; Siwek-Wilczyńska, K.; Sodan, U.; Teh, K. M.; Trzaska, M.; Wang, G. S.; Wessels, J. P.; Wienold, T.; Wisniewski, K.; Wohlfarth, D.; Zhilin, A.; Hartnack, C.; FOPI Collaboration
1997-02-01
Azimuthal distributions of charged particles and intermediate mass fragments emitted in Au+Au collisions at 600 A MeV have been measured using the FOPI facility at GSI-Darmstadt. Data show a strong increase of the in-plane azimuthal anisotropy ratio with the charge of the detected fragment. Intermediate mass fragments are found to exhibit a strong momentum-space alignment with respect of the reaction plane. The experimental results are presented as a function of the polar centre-of-mass angle and over a broad range of impact parameters. They are compared to the predictions of the Isospin Quantum Molecular Dynamics model using three different parametrisations of the equation of state. We show that such highly accurate data provide stringent test for microscopic transport models and can potentially constrain separately the stiffness of the nuclear equation of state and the momentum dependence of the nuclear interaction.
In situ bending of layered compounds : The role of anisotropy in Ti2AlC microcantilevers
Yang, Huajie; Zhang, Peng; Pei, Yutao; Zhang, Zhefeng; De Hosson, Jeff Th. M.
2014-01-01
The paper concentrates on in situ bending tests and analysis of the failure of materials exhibiting strong anisotropy. As a typical example, Ti2AlC microcantilevers (MCs) were scrutinized. The anisotropic flexural strength of Ti2AlC MCs was measured, and the strength of the strong orientation was fo
The expected anisotropy in solid inflation
Energy Technology Data Exchange (ETDEWEB)
Bartolo, Nicola; Ricciardone, Angelo [Dipartimento di Fisica e Astronomia ' ' G. Galilei' ' , Università degli Studi di Padova, via Marzolo 8, I-35131, Padova (Italy); Peloso, Marco; Unal, Caner, E-mail: nicola.bartolo@pd.infn.it, E-mail: peloso@physics.umn.edu, E-mail: angelo.ricciardone@pd.infn.it, E-mail: unal@physics.umn.edu [School of Physics and Astronomy, University of Minnesota, 116 Church Street S.E., Minneapolis 55455 (United States)
2014-11-01
Solid inflation is an effective field theory of inflation in which isotropy and homogeneity are accomplished via a specific combination of anisotropic sources (three scalar fields that individually break isotropy). This results in specific observational signatures that are not found in standard models of inflation: a non-trivial angular dependence for the squeezed bispectrum, and a possibly long period of anisotropic inflation (to drive inflation, the ''solid'' must be very insensitive to any deformation, and thus background anisotropies are very slowly erased). In this paper we compute the expected level of statistical anisotropy in the power spectrum of the curvature perturbations of this model. To do so, we account for the classical background values of the three scalar fields that are generated on large (superhorizon) scales during inflation via a random walk sum, as the perturbation modes leave the horizon. Such an anisotropy is unavoidably generated, even starting from perfectly isotropic classical initial conditions. The expected level of anisotropy is related to the duration of inflation and to the amplitude of the squeezed bispectrum. If this amplitude is close to its current observational limit (so that one of the most interesting predictions of the model can be observed in the near future), we find that a level of statistical anisotropy F{sup 2} gives frozen and scale invariant vector perturbations on superhorizon scales.
Essentials of nonlinear optics
Murti, Y V G S
2014-01-01
Current literature on Nonlinear Optics varies widely in terms of content, style, and coverage of specific topics, relative emphasis of areas and the depth of treatment. While most of these books are excellent resources for the researchers, there is a strong need for books appropriate for presenting the subject at the undergraduate or postgraduate levels in Universities. The need for such a book to serve as a textbook at the level of the bachelors and masters courses was felt by the authors while teaching courses on nonlinear optics to students of both science and engineering during the past two decades. This book has emerged from an attempt to address the requirement of presenting the subject at college level. A one-semester course covering the essentials can effectively be designed based on this.
Monte Carlo and nonlinearities
Dauchet, Jérémi; Blanco, Stéphane; Caliot, Cyril; Charon, Julien; Coustet, Christophe; Hafi, Mouna El; Eymet, Vincent; Farges, Olivier; Forest, Vincent; Fournier, Richard; Galtier, Mathieu; Gautrais, Jacques; Khuong, Anaïs; Pelissier, Lionel; Piaud, Benjamin; Roger, Maxime; Terrée, Guillaume; Weitz, Sebastian
2016-01-01
The Monte Carlo method is widely used to numerically predict systems behaviour. However, its powerful incremental design assumes a strong premise which has severely limited application so far: the estimation process must combine linearly over dimensions. Here we show that this premise can be alleviated by projecting nonlinearities on a polynomial basis and increasing the configuration-space dimension. Considering phytoplankton growth in light-limited environments, radiative transfer in planetary atmospheres, electromagnetic scattering by particles and concentrated-solar-power-plant productions, we prove the real world usability of this advance on four test-cases that were so far regarded as impracticable by Monte Carlo approaches. We also illustrate an outstanding feature of our method when applied to sharp problems with interacting particles: handling rare events is now straightforward. Overall, our extension preserves the features that made the method popular: addressing nonlinearities does not compromise o...
Energy Technology Data Exchange (ETDEWEB)
Ngo, D.-T., E-mail: ndthe82@gmail.com [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Meng, Z.L. [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Tahmasebi, T. [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Data Storage Institute, A-STAR (Agency for Science Technology and Research), 5 Engineering Drive 1, Singapore 117608 (Singapore); Yu, X. [Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603 (Singapore); Thoeng, E. [Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603 (Singapore); Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Yeo, L.H. [Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Rusydi, A., E-mail: phyandri@nus.edu.sg [Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603 (Singapore); Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Han, G.C [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Teo, K.-L., E-mail: eleteokl@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore)
2014-01-15
We report on a strong perpendicular magnetic anisotropy in [CoFe 0.4 nm/Pd t]{sub 6} (t=1.0–2.0 nm) multilayers fabricated by DC sputtering in an ultrahigh vacuum chamber. Saturation magnetization, M{sub s}, and uniaxial anisotropy, K{sub u}, of the multilayers decrease with increasing the spacing thickness; with a M{sub s} of 155 emu/cc and a K{sub u} of 1.14×10{sup 5} J/m{sup 3} at a spacing thickness of t=2 nm. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements reveal that spin and orbital magnetic moments of Co and Fe in CoFe film decrease as a function of Pd thickness, indicating the major contribution of surface/interfacial magnetism to the magnetic properties of the film. - Highlights: • Strong perpendicular magnetic anisotropy essentially contributed by interfacial anisotropy. • Controllably magnetic properties with low M{sub s}, high K{sub u}, high P. • Interfacial magnetic moments modified by CoFe/Pd interfaces with strong spin–orbit coupling. • Narrow Bloch walls with Néel caps. • Superior magnetic characteristics for spin-torque applications.
Das, Ritima; Rai, S. S.
2017-01-01
We use Rayleigh and Love wave empirical Green's function (EGF) recovered from the cross correlation of seismic ambient noise to study the spatial distribution of radial anisotropy in the southern India crust. The corresponding dispersion curves in the period 2 to 32 s are measured from ambient noise data recorded at 57 sites, and the strength of anisotropy computed from the discrepancy between shear velocities obtained from Rayleigh (VSV) and Love (VSH) at various depths down to 40 km. In upper crust (up to a depth of 20 km) the region is characterized by anisotropy coefficients of - 2 to + 2% that could be explained due to a combination of fluid-filled open cracks and foliated metamorphic rocks. At deeper levels (beyond 20 km), except for the Archean metamorphic terrain, most part of south India has anisotropies of up to 5%. This may be due to rocks with varying degree of metamorphism. Beneath the Archean metamorphic terrain, the anisotropy is recorded up to 9% in the depth range of 20-40 km. This high anisotropy is unlikely to be the manifestation of any recent geodynamic process, considering that the region has low surface heat flow ( 30 mW/m2). We propose that the observed strong anisotropy in the metamorphic belt of southern India crust could best be explained as due to the presence of micaceous minerals or amphiboles in the deep crust that are formed possibly during the evolution of granulite terrain at 2.5 Ga.
Bale, S D; Howes, G G; Quataert, E; Salem, C; Sundkvist, D
2009-01-01
The proton temperature anisotropy in the solar wind is known to be constrained by the theoretical thresholds for pressure anisotropy-driven instabilities. Here we use approximately 1 million independent measurements of gyroscale magnetic fluctuations in the solar wind to show for the first time that these fluctuations are enhanced along the temperature anisotropy thresholds of the mirror, proton oblique firehose, and ion cyclotron instabilities. In addition, the measured magnetic compressibility is enhanced at high plasma beta ($\\beta_\\parallel \\gtrsim 1$) along the mirror instability threshold but small elsewhere, consistent with expectations of the mirror mode. The power in this frequency (the 'dissipation') range is often considered to be driven by the solar wind turbulent cascade, an interpretation which should be qualified in light of the present results. In particular, we show that the short wavelength magnetic fluctuation power is a strong function of collisionality, which relaxes the temperature aniso...
Magnetic anisotropy, damping, and interfacial spin transport in Pt/LSMO bilayers
Directory of Open Access Journals (Sweden)
H. K. Lee
2016-05-01
Full Text Available We report ferromagnetic resonance measurements of magnetic anisotropy and damping in epitaxial La0.7Sr0.3MnO3 (LSMO and Pt capped LSMO thin films on SrTiO3 (001 substrates. The measurements reveal large negative perpendicular magnetic anisotropy and a weaker uniaxial in-plane anisotropy that are unaffected by the Pt cap. The Gilbert damping of the bare LSMO films is found to be low α = 1.9(1 × 10−3, and two-magnon scattering is determined to be significant and strongly anisotropic. The Pt cap increases the damping by 50% due to spin pumping, which is also directly detected via inverse spin Hall effect in Pt. Our work demonstrates efficient spin transport across the Pt/LSMO interface.
Venters, T. M.; Pavlidou, V.
2013-01-01
The intergalactic magnetic field (IGMF) may leave an imprint on the angular anisotropy of the extragalactic gamma-ray background through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragalactic background light. A strong IGMF will deflect secondary particles produced in these cascades and will thus tend to isotropize lower energy cascade photons, thereby inducing a modulation in the anisotropy energy spectrum of the gamma-ray background. Here we present a simple, proof-of-concept calculation of the magnitude of this effect and demonstrate that current Fermi data already seem to prefer nonnegligible IGMF values. The anisotropy energy spectrum of the Fermi gamma-ray background could thus be used as a probe of the IGMF strength.
2015-01-01
From the Back Cover: The emphasis throughout the present volume is on the practical application of theoretical mathematical models helping to unravel the underlying mechanisms involved in processes from mathematical physics and biosciences. It has been conceived as a unique collection of abstract methods dealing especially with nonlinear partial differential equations (either stationary or evolutionary) that are applied to understand concrete processes involving some important applications re...
Electrophoresis in strong electric fields.
Barany, Sandor
2009-01-01
Two kinds of non-linear electrophoresis (ef) that can be detected in strong electric fields (several hundred V/cm) are considered. The first ("classical" non-linear ef) is due to the interaction of the outer field with field-induced ionic charges in the electric double layer (EDL) under conditions, when field-induced variations of electrolyte concentration remain to be small comparatively to its equilibrium value. According to the Shilov theory, the non-linear component of the electrophoretic velocity for dielectric particles is proportional to the cubic power of the applied field strength (cubic electrophoresis) and to the second power of the particles radius; it is independent of the zeta-potential but is determined by the surface conductivity of particles. The second one, the so-called "superfast electrophoresis" is connected with the interaction of a strong outer field with a secondary diffuse layer of counterions (space charge) that is induced outside the primary (classical) diffuse EDL by the external field itself because of concentration polarization. The Dukhin-Mishchuk theory of "superfast electrophoresis" predicts quadratic dependence of the electrophoretic velocity of unipolar (ionically or electronically) conducting particles on the external field gradient and linear dependence on the particle's size in strong electric fields. These are in sharp contrast to the laws of classical electrophoresis (no dependence of V(ef) on the particle's size and linear dependence on the electric field gradient). A new method to measure the ef velocity of particles in strong electric fields is developed that is based on separation of the effects of sedimentation and electrophoresis using videoimaging and a new flowcell and use of short electric pulses. To test the "classical" non-linear electrophoresis, we have measured the ef velocity of non-conducting polystyrene, aluminium-oxide and (semiconductor) graphite particles as well as Saccharomice cerevisiae yeast cells as a
Nonlinear optical interactions in silicon waveguides
Kuyken, B.; Leo, F.; Clemmen, S.; Dave, U.; Van Laer, R.; Ideguchi, T.; Zhao, H.; Liu, X.; Safioui, J.; Coen, S.; Gorza, S. P.; Selvaraja, S. K.; Massar, S.; Osgood, R. M.; Verheyen, P.; Van Campenhout, J.; Baets, R.; Green, W. M. J.; Roelkens, G.
2017-03-01
The strong nonlinear response of silicon photonic nanowire waveguides allows for the integration of nonlinear optical functions on a chip. However, the detrimental nonlinear optical absorption in silicon at telecom wavelengths limits the efficiency of many such experiments. In this review, several approaches are proposed and demonstrated to overcome this fundamental issue. By using the proposed methods, we demonstrate amongst others supercontinuum generation, frequency comb generation, a parametric optical amplifier, and a parametric optical oscillator.
Interpreting Power Anisotropy Measurements in Plasma Turbulence
Chen, C H K; Horbury, T S; Schekochihin, A A
2009-01-01
A relationship between power anisotropy and wavevector anisotropy in turbulent fluctuations is derived. This can be used to interpret plasma turbulence measurements, for example in the solar wind. If fluctuations are anisotropic in shape then the ion gyroscale break point in spectra in the directions parallel and perpendicular to the magnetic field would not occur at the same frequency, and similarly for the electron gyroscale break point. This is an important consideration when interpreting solar wind observations in terms of anisotropic turbulence theories. Model magnetic field power spectra are presented assuming a cascade of critically balanced Alfven waves in the inertial range and kinetic Alfven waves in the dissipation range. The variation of power anisotropy with scale is compared to existing solar wind measurements and the similarities and differences are discussed.
The expected anisotropy in solid inflation
Bartolo, Nicola; Ricciardone, Angelo; Unal, Caner
2014-01-01
Solid inflation is an effective field theory of inflation in which isotropy and homogeneity are accomplished via a specific combination of anisotropic sources (three scalar fields that individually break isotropy). This results in specific observational signatures that are not found in standard models of inflation: a non-trivial angular dependence for the squeezed bispectrum, and a possibly long period of anisotropic inflation (to drive inflation, the "solid" must be very insensitive to any deformation, and thus background anisotropies are very slowly erased). In this paper we compute the expected level of statistical anisotropy in the power spectrum of the curvature perturbations of this model. To do so, we account for the classical background values of the three scalar fields that are generated on large (superhorizon) scales during inflation via a random walk sum, as the perturbation modes leave the horizon. Such an anisotropy is unavoidably generated, even starting from perfectly isotropic classical initia...
Psychophysics and the anisotropy of time.
Riemer, Martin
2015-12-15
In psychophysics, experimental control over the presented stimuli is an important prerequisite. Due to the anisotropy of time, this prerequisite is not given in psychophysical experiments on time perception. Many important factors (e.g., the direction of perceived time flow) cannot be manipulated in timing experiments. The anisotropy of time is a peculiarity, which distinguishes the time dimension from other perceptual qualities. Here I summarize the anisotropy-related differences between the perception of time and the perception of other qualities. It is discussed to what extent these differences might affect results and interpretations in psychophysical experiments. In conclusion, I argue for a 'view from nowhen' on the psychophysical study of time perception. Copyright © 2015 Elsevier Inc. All rights reserved.
CMB Anisotropies Total Angular Momentum Method
Hu, W; Hu, Wayne; White, Martin
1997-01-01
A total angular momentum representation simplifies the radiation transport problem for temperature and polarization anisotropy in the CMB. Scattering terms couple only the quadrupole moments of the distributions and each moment corresponds directly to the observable angular pattern on the sky. We develop and employ these techniques to study the general properties of anisotropy generation from scalar, vector and tensor perturbations to the metric and the matter, both in the cosmological fluids and from any seed perturbations (e.g.~defects) that may be present. The simpler, more transparent form and derivation of the Boltzmann equations brings out the geometric and model-independent aspects of temperature and polarization anisotropy formation. Large angle scalar polarization provides a robust means to distinguish between isocurvature and adiabatic models for structure formation in principle. Vector modes have the unique property that the CMB polarization is dominated by magnetic type parity at small angles and ...
Radial anisotropy ambient noise tomography of volcanoes
Mordret, Aurélien; Rivet, Diane; Shapiro, Nikolai; Jaxybulatov, Kairly; Landès, Matthieu; Koulakov, Ivan; Sens-Schönfelder, Christoph
2016-04-01
The use of ambient seismic noise allows us to perform surface-wave tomography of targets which could hardly be imaged by other means. The frequencies involved (~ 0.5 - 20 s), somewhere in between active seismic and regular teleseismic frequency band, make possible the high resolution imaging of intermediate-size targets like volcanic edifices. Moreover, the joint inversion of Rayleigh and Love waves dispersion curves extracted from noise correlations allows us to invert for crustal radial anisotropy. We present here the two first studies of radial anisotropy on volcanoes by showing results from Lake Toba Caldera, a super-volcano in Indonesia, and from Piton de la Fournaise volcano, a hot-spot effusive volcano on the Réunion Island (Indian Ocean). We will see how radial anisotropy can be used to infer the main fabric within a magmatic system and, consequently, its dominant type of intrusion.
Rajapitamahuni, A; Zhang, L; Koten, M A; Singh, V R; Burton, J D; Tsymbal, E Y; Shield, J E; Hong, X
2016-05-06
The relatively low magnetocrystalline anisotropy (MCA) in strongly correlated manganites (La,Sr)MnO_{3} has been a major hurdle for implementing them in spintronic applications. Here we report an unusual, giant enhancement of in-plane MCA in 6 nm La_{0.67}Sr_{0.33}MnO_{3} (LSMO) films grown on (001) SrTiO_{3} substrates when the top 2 nm is patterned into periodic stripes of 100 or 200 nm width. Planar Hall effect measurements reveal an emergent uniaxial anisotropy superimposed on one of the original biaxial easy axes for unpatterned LSMO along ⟨110⟩ directions, with a 50-fold enhanced anisotropy energy density of 5.6×10^{6} erg/cm^{3} within the nanostripes, comparable to the value for cobalt. The magnitude and direction of the uniaxial anisotropy exclude shape anisotropy and the step edge effect as its origin. High resolution transmission electron microscopy studies reveal a nonequilibrium strain distribution and drastic suppression in the c-axis lattice constant within the nanostructures, which is the driving mechanism for the enhanced uniaxial MCA, as suggested by first-principles density functional calculations.
Energy Technology Data Exchange (ETDEWEB)
Reichhardt, Charles [Los Alamos National Laboratory; Reichhardt, Cynthia [Los Alamos National Laboratory
2008-01-01
We show using simulations that when interstitial vortices are present in superconductors with periodic pinning arrays, the transport in two perpendicular directions can be anisotropic. The degree of the anisotropy varies as a function of field due to the fact that the interstitial vortex lattice has distinct orderings at different matching fields. The anisotropy is most pronounced at the matching fields but persists at incommensurate fields, and it is most prominent for triangular, honeycomb, and kagome pinning arrays. Square pinning arrays can also show anisotropic transport at certain fields in spite of the fact that the perpendicular directions of the square pinning array are identical. We show that the anisotropy results from distinct vortex dynamical states and that although the critical depinning force may be lower in one direction, the vortex velocity above depinning may also be lower in the same direction for ranges of external drives where both directions are depinned. For honeycomb and kagome pinning arrays, the anisotropy can show multiple reversals as a function of field. We argue that when the pinning sites can be multiply occupied such that no interstitial vortices are present, the anisotropy is strongly reduced or absent.
Super-weak asthenosphere models in light of plate motions and azimuthal anisotropy
Becker, T. W.
2016-12-01
Plate motions and azimuthal seismic anisotropy from surface waves are consistent with a strong, oceanic lithosphere that is predominantly dragged by slabs, and weakened upon subduction. Plates are underlain and sustained by a moderately weak asthenosphere, as expected from the temperature and pressure dependence of olivine viscosity for the upper mantle. However, recent observations from active source seismology, magneto-tellurics, body wave anisotropy, and postseismic surface deformation can be interpreted to imply the existence of a very weak channel of low viscosity material, potentially decoupling plates, not unlike a plume-fed asthenosphere scenario in several ways. Here, I explore the implications of such a decoupling channel for plate driving forces as well as observations of seismic anisotropy. The thickness and viscosity reduction of the channel are expected to trade off with each other, and plate motions are sensitive to the lateral extent of this super-weak asthenosphere. While there is some ambiguity of plate motion metrics with the strength of slabs, seismic anisotropy is expected to be sensitive to how shear is localized with depth. The overall good fit of azimuthal anisotropy patterns to flow model predictions brakes down for a number of the more extreme lateral and depth-dependent viscosity scenarios. This may imply that weakening mechanisms may not apply globally under plates, but are rather limited to isolated regions, perhaps associated with melt rich pockets that have limited connectivity.
Rajapitamahuni, A.; Zhang, L.; Koten, M. A.; Singh, V. R.; Burton, J. D.; Tsymbal, E. Y.; Shield, J. E.; Hong, X.
2016-05-01
The relatively low magnetocrystalline anisotropy (MCA) in strongly correlated manganites (La ,Sr )MnO3 has been a major hurdle for implementing them in spintronic applications. Here we report an unusual, giant enhancement of in-plane MCA in 6 nm La0.67Sr0.33MnO3 (LSMO) films grown on (001) SrTiO3 substrates when the top 2 nm is patterned into periodic stripes of 100 or 200 nm width. Planar Hall effect measurements reveal an emergent uniaxial anisotropy superimposed on one of the original biaxial easy axes for unpatterned LSMO along ⟨110 ⟩ directions, with a 50-fold enhanced anisotropy energy density of 5.6 ×106 erg /cm3 within the nanostripes, comparable to the value for cobalt. The magnitude and direction of the uniaxial anisotropy exclude shape anisotropy and the step edge effect as its origin. High resolution transmission electron microscopy studies reveal a nonequilibrium strain distribution and drastic suppression in the c -axis lattice constant within the nanostructures, which is the driving mechanism for the enhanced uniaxial MCA, as suggested by first-principles density functional calculations.
Hydraulic Conductivity Anisotropy of Heterogeneous Unsaturated Soils
Sun, Dongmin; Zhu, Jianting
2010-05-01
The effects of saturation degree (or capillary pressure) on hydraulic conductivity anisotropy in unsaturated soils have not been fully understood. This study developed an approach based on a conceptualization of combining the neural network based pedo-transfer function (PTF) results with the thin layer concept to explore the capillary pressure-dependent anisotropy in relation to soil texture and soil bulk density. The main objective is to examine how anisotropy characteristics are related to the relationships between hydraulic parameters and the basic soil attributes such as texture and bulk density. The hydraulic parameters are correlated with the texture and bulk density based on the pedo-transfer function (PTF) results. It is demonstrated that non-monotonic behavior of the unsaturated soil anisotropy in relation to the capillary pressure is only observed when the saturated hydraulic conductivity and the shape parameter are both related to the mean particle diameter. When only one hydraulic parameter is related to the grain diameter or when both are not related to the same attribute simultaneously, the unsaturated soil anisotropy increases monotonically with the increasing capillary pressure head. Therefore, it is suggested that this behavior is mainly due to the coupled dependence of the layer saturated hydraulic conductivities and the shape factors on the texture and bulk density. The correlation between the soil grain diameter and bulk density decreases the anisotropy effects of the unsaturated layered soils. The study illustrates that the inter-relationships of soil texture, bulk density, and hydraulic properties may cause vastly different characteristics of anisotropic unsaturated soils.
Nonlinear plasmonics at high temperatures
Directory of Open Access Journals (Sweden)
Sivan Yonatan
2017-01-01
Full Text Available We solve the Maxwell and heat equations self-consistently for metal nanoparticles under intense continuous wave (CW illumination. Unlike previous studies, we rely on experimentally-measured data for metal permittivity for increasing temperature and for the visible spectral range. We show that the thermal nonlinearity of the metal can lead to substantial deviations from the predictions of the linear model for the temperature and field distribution and, thus, can explain qualitatively the strong nonlinear scattering from such configurations observed experimentally. We also show that the incompleteness of existing data of the temperature dependence of the thermal properties of the system prevents reaching a quantitative agreement between the measured and calculated scattering data. This modeling approach is essential for the identification of the underlying physical mechanism responsible for the thermo-optical nonlinearity of the metal and should be adopted in all applications of high-temperature nonlinear plasmonics, especially for refractory metals, for both CW and pulsed illumination.
Nonlinear plasmonics at high temperatures
Sivan, Yonatan; Chu, Shi-Wei
2017-01-01
We solve the Maxwell and heat equations self-consistently for metal nanoparticles under intense continuous wave (CW) illumination. Unlike previous studies, we rely on experimentally-measured data for metal permittivity for increasing temperature and for the visible spectral range. We show that the thermal nonlinearity of the metal can lead to substantial deviations from the predictions of the linear model for the temperature and field distribution and, thus, can explain qualitatively the strong nonlinear scattering from such configurations observed experimentally. We also show that the incompleteness of existing data of the temperature dependence of the thermal properties of the system prevents reaching a quantitative agreement between the measured and calculated scattering data. This modeling approach is essential for the identification of the underlying physical mechanism responsible for the thermo-optical nonlinearity of the metal and should be adopted in all applications of high-temperature nonlinear plasmonics, especially for refractory metals, for both CW and pulsed illumination.
Measuring the Alfvénic Nature of the Interstellar Medium: Velocity Anisotropy Revisited
Burkhart, Blakesley; Lazarian, A.; Leão, I. C.; de Medeiros, J. R.; Esquivel, A.
2014-08-01
The dynamics of the interstellar medium (ISM) are strongly affected by turbulence, which shows increased anisotropy in the presence of a magnetic field. We expand upon the Esquivel & Lazarian method to estimate the Alfvén Mach number using the structure function anisotropy in velocity centroid data from Position-Position-Velocity maps. We utilize three-dimensional magnetohydrodynamic simulations of fully developed turbulence, with a large range of sonic and Alfvénic Mach numbers, to produce synthetic observations of velocity centroids with observational characteristics such as thermal broadening, cloud boundaries, noise, and radiative transfer effects of carbon monoxide. In addition, we investigate how the resulting anisotropy-Alfvén Mach number dependency found in Esquivel & Lazarian might change when taking the second moment of the Position-Position-Velocity cube or when using different expressions to calculate the velocity centroids. We find that the degree of anisotropy is related primarily to the magnetic field strength (i.e., Alfvén Mach number) and the line-of-sight orientation, with a secondary effect on sonic Mach number. If the line of sight is parallel to up to ≈45 deg off of the mean field direction, the velocity centroid anisotropy is not prominent enough to distinguish different Alfvénic regimes. The observed anisotropy is not strongly affected by including radiative transfer, although future studies should include additional tests for opacity effects. These results open up the possibility of studying the magnetic nature of the ISM using statistical methods in addition to existing observational techniques.
Measuring the Alfvénic nature of the interstellar medium: Velocity anisotropy revisited
Energy Technology Data Exchange (ETDEWEB)
Burkhart, Blakesley; Lazarian, A. [Astronomy Department, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706-1582 (United States); Leão, I. C.; De Medeiros, J. R. [Departamento de Fsica Teórica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 (Brazil); Esquivel, A. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543,04510 Mexico D.F. (Mexico)
2014-08-01
The dynamics of the interstellar medium (ISM) are strongly affected by turbulence, which shows increased anisotropy in the presence of a magnetic field. We expand upon the Esquivel and Lazarian method to estimate the Alfvén Mach number using the structure function anisotropy in velocity centroid data from Position-Position-Velocity maps. We utilize three-dimensional magnetohydrodynamic simulations of fully developed turbulence, with a large range of sonic and Alfvénic Mach numbers, to produce synthetic observations of velocity centroids with observational characteristics such as thermal broadening, cloud boundaries, noise, and radiative transfer effects of carbon monoxide. In addition, we investigate how the resulting anisotropy-Alfvén Mach number dependency found in Esquivel and Lazarian might change when taking the second moment of the Position-Position-Velocity cube or when using different expressions to calculate the velocity centroids. We find that the degree of anisotropy is related primarily to the magnetic field strength (i.e., Alfvén Mach number) and the line-of-sight orientation, with a secondary effect on sonic Mach number. If the line of sight is parallel to up to ≈45 deg off of the mean field direction, the velocity centroid anisotropy is not prominent enough to distinguish different Alfvénic regimes. The observed anisotropy is not strongly affected by including radiative transfer, although future studies should include additional tests for opacity effects. These results open up the possibility of studying the magnetic nature of the ISM using statistical methods in addition to existing observational techniques.
Anisotropy of the Topopah Spring Member Tuff
Energy Technology Data Exchange (ETDEWEB)
Martin, R.J. III; Boyd, P.J.; Haupt, R.W. [New England Research, Inc., White River Junction, VT (United States); Price, R.H. [Sandia National Labs., Albuquerque, NM (United States)
1992-07-01
Mechanical properties of the tuffaceous rocks within Yucca Mountain are needed for near and far-field modeling of the potential nuclear waste repository. If the mechanical properties are significantly anisotropic (i.e., direction-dependent), a more complex model is required. Relevant data from tuffs tested in earlier studies indicate that elastic and strength properties are anisotropic. This scoping study confirms the elastic anisotropy and concludes some tuffs are transversely isotropic. An approach for sampling and testing the rock to determine the magnitude of the anisotropy is proposed.
Mobility anisotropy of two-dimensional semiconductors
Lang, Haifeng; Zhang, Shuqing; Liu, Zhirong
2016-12-01
The carrier mobility of anisotropic two-dimensional semiconductors under longitudinal acoustic phonon scattering was theoretically studied using deformation potential theory. Based on the Boltzmann equation with the relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was derived, showing that the influence of effective mass on mobility anisotropy is larger than those of deformation potential constant or elastic modulus. Parameters were collected for various anisotropic two-dimensional materials (black phosphorus, Hittorf's phosphorus, BC2N , MXene, TiS3, and GeCH3) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio is overestimated by the previously described method.
Mobility anisotropy of two-dimensional semiconductors
Lang, Haifeng; Liu, Zhirong
2016-01-01
The carrier mobility of anisotropic two-dimensional (2D) semiconductors under longitudinal acoustic (LA) phonon scattering was theoretically studied with the deformation potential theory. Based on Boltzmann equation with relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was deduced, which shows that the influence of effective mass to the mobility anisotropy is larger than that of deformation potential constant and elastic modulus. Parameters were collected for various anisotropic 2D materials (black phosphorus, Hittorf's phosphorus, BC$_2$N, MXene, TiS$_3$, GeCH$_3$) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio was overestimated in the past.
Galceran, Regina; López-Mir, Laura; Bozzo, Bernat; Cisneros-Fernández, José; Santiso, José; Balcells, Lluís; Frontera, Carlos; Martínez, Benjamín
2016-04-01
Ferromagnetic insulating L a2CoMn O6 -ɛ (LCMO) epitaxial thin films grown on top of SrTi O3 (001) substrates present a strong magnetic anisotropy favoring the out-of-plane (OP) orientation of the magnetization with a large anisotropy field (˜70 kOe for film thickness of about 15 nm). Diminishing oxygen off-stoichiometry of the film enhances the anisotropy. We attribute this to the concomitant shrinkage of the OP cell parameter and to the increasing of the tensile strain of the films. Consistently, LCMO films grown on (LaAlO3)0.3(Sr2AlTaO6) 0.7 and LaAl O3 substrates (with a larger OP lattice parameter and compressive stress) display in-plane (IP) magnetic anisotropy. Thus, we link the strong magnetic anisotropy observed in LCMO to the film stress: tensile strain favors perpendicular anisotropy, and compressive stress favors IP anisotropy. We also report on the thickness dependence of the magnetic properties. Perpendicular anisotropy, saturation magnetization, and Curie temperature are maintained over a large range of film thickness.