Anisotropic Transfer Research Articles

Logarithmic violation of scaling in strongly anisotropic turbulent transfer of a passive vector field.

Inertial-range asymptotic behavior of a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow, is studied by means of the field-theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, not correlated in time, with the pair correlation function of the form ∝δ(t-t')/k(⊥)(d-1+ξ), where k(⊥)=|k(⊥)| and k(⊥) is the component of the wave vector, perpendicular to the distinguished direction ("direction of the flow")--the d-dimensional generalization of the ensemble introduced by Avellaneda and Majda [Commun. Math. Phys. 131, 381 (1990)]. The stochastic advection-diffusion equation for the transverse (divergence-free) vector field includes, as special cases, the kinematic dynamo model for magnetohydrodynamic turbulence and the linearized Navier-Stokes equation. In contrast to the well-known isotropic Kraichnan's model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the dependence on the integral turbulence scale L has a logarithmic behavior: Instead of powerlike corrections to ordinary scaling, determined by naive (canonical) dimensions, the anomalies manifest themselves as polynomials of logarithms of L. The key point is that the matrices of scaling dimensions of the relevant families of composite operators appear nilpotent and cannot be diagonalized. The detailed proof of this fact is given for the correlation functions of arbitrary order.

Mesoscale morphology evolution of a GdAl3(BO3)4single crystal in a flux system: a case study of thermodynamic control of the anisotropic mass transfer during crystal growth

In the flux system of GdAl3(BO3)4, the compromise in competition between thermodynamic and kinetic control on the mass transfer has been studied from the viewpoint of chemical engineering. Different control mechanisms on the mass transfer in the melt growth system result in various mesoscale morphologies of a single crystal. Both the calculated and experimental results demonstrate thermodynamic control of the anisotropic mass transfer during crystal growth, leading to the mesoscale morphology evolution of the GdAl3(BO3)4 single crystal similar to the matryoshka. The present work can deepen our understanding of mesoscale morphology evolution of the GdAl3(BO3)4 single crystal in the flux growth system.

Vector Fourier optics of anisotropic materials

The Fourier optics technique is founded on the transfer function derived from the scalar wave equation and thus has traditionally been applied to monochromatic scalar fields propagating paraxially in isotropic lossless materials. We review scalar and vector diffraction theory to show that the scalar Fourier optics technique can be seamlessly extended to the case of time-dependent nonparaxial and evanescent vector fields propagating in anisotropic and/or absorbing materials. The missing piece is shown to be the Fourier-domain vector boundary conditions that have recently been derived from the real-domain vector Rayleigh–Sommerfeld diffraction integral. These boundary conditions, complemented by the anisotropic transfer functions provided by the roots of the Booker quartic, combine the rigor of Green’s function integrals with the intuitive simplicity and general applicability of Fourier optics. We illustrate the power of this technique via analytically simple solutions to traditionally complex problems such as Fresnel transmission between arbitrary media, uniaxial conoscopy, and biaxial conical refraction. The accuracy of vector near-field diffraction is validated via comparison with the finite-difference time-domain method.

Anisotropic pattern transfer in ultrananocrystalline diamond films by inductively coupled plasma etching.

High density plasma etching of ultrananocrystalline diamond (UNCD) films wasperformed in O2 and O2/Ar inductively coupled plasma (ICP) discharges. The O2/Ar ICP discharges produced higher etch rates due to enhanced physical component of the etching, and a maximum etch rate of -280 nm/min was obtained in 10 sccm O2/5 sccm Ar discharges. Very high etch selectivities up to -140:1 were obtained for the UNCD over Al mask layer. Anisotropic pattern transfer with a vertical sidewall profile was achieved in the 10 sccm O2/5 sccm Ar discharges at a relatively low source power (300 W) and a moderate rf chuck power (200 W).

Anisotropic energy transfers in quasi-static magnetohydrodynamic turbulence

We perform direct numerical simulations of quasi-static magnetohydrodynamic turbulence and compute various energy transfers including the ring-to-ring and conical energy transfers, and the energy fluxes of the perpendicular and parallel components of the velocity field. We show that the rings with higher polar angles transfer energy to ones with lower polar angles. For large interaction parameters, the dominant energy transfer takes place near the equator (polar angle θ≈π2). The energy transfers are local both in wavenumbers and angles. The energy flux of the perpendicular component is predominantly from higher to lower wavenumbers (inverse cascade of energy), while that of the parallel component is from lower to higher wavenumbers (forward cascade of energy). Our results are consistent with earlier results, which indicate quasi two-dimensionalization of quasi-static magnetohydrodynamic flows at high interaction parameters.

Interpretation of coastal wind transfer functions with momentum balances derived from idealized numerical model simulations

The local wind-driven circulation off southern San Diego is addressed with two complementary statistical and dynamical frameworks based on observations and idealized numerical model simulations. The observations including surface currents from high-frequency radars, subsurface currents from a nearshore mooring, and wind records at a local wind station are analyzed with the idealized ocean model (MITgcm) simulations using realistic bottom topography and spatially uniform wind stress forcing. Statistically estimated anisotropic local wind transfer functions characterize the observed oceanic spectral response to wind stress separately in the x (east-west) and y (north-south) directions. We delineate the coastal circulation at three primary frequencies [low (σ L=0.0767 cycles per day (cpd)), diurnal (σ D=1 cpd), and inertial (σ f=1.07 cpd) frequencies] with the momentum budget equations and transfer functions. At low frequency, the magnitudes of transfer functions are enhanced near the coast, attributed to geostrophic balance between wind-driven pressure gradients and the Coriolis force on currents. The response diminishes away from the coast, returning to the balance between frictional and Coriolis terms, as in the classic Ekman model. On the contrary, transfer functions in the near-inertial frequency band show reduced magnitudes near the coast primarily due to friction, but exhibits the enhanced seaward response as a result of the inertial resonance. The idealized model simulations forced by local wind stress can identify the influences of remote wind stress and the biases in the data-derived transfer functions.

Large-scale anisotropy in stably stratified rotating flows.

We present results from direct numerical simulations of the Boussinesq equations in the presence of rotation and/or stratification, both in the vertical direction. The runs are forced isotropically and randomly at small scales and have spatial resolutions of up to 1024(3) grid points and Reynolds numbers of ≈1000. We first show that solutions with negative energy flux and inverse cascades develop in rotating turbulence, whether or not stratification is present. However, the purely stratified case is characterized instead by an early-time, highly anisotropic transfer to large scales with almost zero net isotropic energy flux. This is consistent with previous studies that observed the development of vertically sheared horizontal winds, although only at substantially later times. However, and unlike previous works, when sufficient scale separation is allowed between the forcing scale and the domain size, the kinetic energy displays a perpendicular (horizontal) spectrum with power-law behavior compatible with ∼k(⊥)(-5/3), including in the absence of rotation. In this latter purely stratified case, such a spectrum is the result of a direct cascade of the energy contained in the large-scale horizontal wind, as is evidenced by a strong positive flux of energy in the parallel direction at all scales including the largest resolved scales.

Strain modulated anisotropic electronic charge transfer in perovskite Pr0.67 Sr0.33 MnO3 thin films

Strain-modulated anisotropic electronic charge transfers in perovskite ${\mathrm{Pr}}_{0.67}$${\mathrm{Sr}}_{0.33}$${\mathrm{MnO}}_{3}$ thin films were investigated using polarization dependent x-ray absorption near-edge structure at the Mn $K$ absorption edge and half-integer diffraction. The strain from the lattice mismatch between the film and the substrate affects the ${\mathrm{MnO}}_{6}$ octahedron tilt pattern in thin films, which modifies the Mn-O bond length and bond angles, and charge transfer properties. The probability of charge transfer from O to Mn is anisotropic along the in-plane and out-of-plane directions, which is enhanced in the direction with compressive strain due to a larger overlap of Mn 3$d$ and O 2$p$ orbitals as a result of a shorter Mn-O bond length. These results were further verified using the ab initio FEFF calculations and Curie temperature calculation.

Magnetically Enhanced Bicelles Delivering Switchable Anisotropy in Optical Gels

Mesostructures responding to external triggers such as temperature, pH, or magnetic field have the potential to be used as self-acting sensors, detectors, or switches. Key features are a strong and well-defined response to the external trigger. Here, we present magnetic alignable bicelles embedded into a gelatin matrix generating magnetically switchable structures, which can reversibly be locked and unlocked by adjusting the temperature. We show that the disk-like aggregates can be orientated in magnetic fields, and such orientation can be preserved after embedding into gelatin. The resulting gel cubes show an anisotropic transfer for electromagnetic waves, i.e., a different spatial birefringence. Cycling through the melting point of gelatin sets the structure back to its isotropic state providing a read-out of the thermal history. Stacking of the bicelles induced by the gelatin promotes magnetic aligning, as an increased aggregation number in the stacks increases the magnetic orientation energy.

The nonlinear optical properties of nanotubes with spiral defects in a longitudinal magnetic field

It is demonstrated that the anisotropic transfer of photon momentum to an electronic subsystem results in induction of a photon-drag EMF in a standing electromagnetic wave along the axis of a nanotube with a spiral defect, which confirms the assumption found in the literature that the occurrence of such an effect in the presence of an external magnetic field is possible not only in 2-D systems but also in nanotubes with a spiral symmetry. One of the potential mechanisms of inducing the EMF connected with the spatial asymmetry of the electron-phonon interaction in a nanotube with a spiral defect is considered. This mechanism allows for such an EMF to occur upon heating the electron system by the Joule heat of the photon-drag current that flows through the nanotube.

Pressure Effects and Orbital Characters in Cuprate and Carbon-Based Superconductors

Pressure effect is overviewed for the cuprates and carbon-based superconductors, with an emphasis on how their orbital characters are modified by pressure. For the high-Tc cuprates, we start from the observation for ambient pressure that, on top of the main orbital (dx 2−y 2), a hybridization with the second (dz 2) orbital around the Fermi energy significantly affects T c in the spin-fluctuation mediated pairing, where the hybridization is dominated by material parameters. We can then show that applying pressures along a, b axes enhances Tc while a c-axis pressure suppresses Tc, where not only the dz 2 hybridization but also Cu(4s) hybridization exert an effect. For the multi-layer cuprates, interlayer pair hopping is suggested to be important, which may contribute to pressure effect. Pressure effect is also interesting in a recently discovered aromatic family of superconductors (picene, etc.). There, we have again multi-band systems, which in this case derive from different molecular orbitals. The Fermi surface is an intriguing composite of different pockets/sheets having different dimensionalities arising from anisotropic transfers between the molecular orbitals, and pressure effects should be an important probe of these.

Investigation of Hole Transporting Properties in Thin-Film and Single-Crystal Organic Field-Effect Transistor Based on Dinaphtho[2,1-b:1',2'-d]thiophene

We describe physicochemical properties, crystal structures, and field-effect transistor performances of dinaphtho[2,1-b:1',2'-d]thiophene (DNT-U) with a unique twisted structure. The HOMO energy level of DNT-U was estimated to be -5.77 eV by measurement of electrochemical property in solution, indicating that this material is a promising candidate for air-stable p-type organic semiconductors. DNT-U possesses anisotropic one-dimensional transfer integrals originating from the columnar face-to-face π-stacking motif, which was determined by X-ray single crystal structural analysis. In order to evaluate intrinsic hole transporting ability of DNT-U, we fabricated the single-crystal field-effect transistors (FETs). The devices showed hole mobility of up to 0.15 cm2 V-1 s-1, which value is almost one order of magnitude higher than that of the vacuum deposited thin film FETs.

A hybrid interface-element for the simulation of moisture-induced cracks in wood

Moisture-induced cracking of wood is a well-known phenomenon. Nevertheless, until now, no numerical approaches are at hand to appropriately capture this feature. Hence, in the framework of this paper, a novel multiphysical hybrid interface-element and a respective interface material formulation are derived in order to be able to coincidentally simulate anisotropic moisture transfer through and along the crack plane and the mechanical response. Hygro-mechanical coupling is considered by means of moisture-dependent input quantities and swelling/shrinkage of the adjacent bulk material. The hybrid element is applied for a comprehensive numerical parameter study on the influence of wood species, material direction and initial moisture content on moisture-induced cracking.

Third-order statistics and the dynamics of strongly anisotropic turbulent flows

Anisotropy is induced by body forces and/or mean large-scale gradients in turbulent flows. For flows without energy production, the dynamics of second-order velocity or second-order vorticity statistics are essentially governed by triple correlations, which are at the origin of the anisotropy that penetrates towards the inertial range, deeply altering the cascade and the eventual dissipation process, with a series of consequences on the evolution of homogeneous turbulence statistics: in the case of rotating turbulence, the anisotropic spectral transfer slaves the multiscale anisotropic energy distribution; nonlinear dynamics are responsible for the linear growth in terms of Ωt of axial integral length-scales; third-order structure functions, derived from velocity triple correlations, exhibit a significant departure from the 4/5 Kolmogorov law. We describe all these implications in detail, starting from the dynamical equations of velocity statistics in Fourier space, which yield third-order correlations at three points (triads) and allow the explicit removal of pressure fluctuations. We first extend the formalism to anisotropic rotating turbulence with ‘production’, in the presence of mean velocity gradients in the rotating frame. Second, we compare the spectral approach at three points to the two-point approach directly performed in physical space, in which we consider the transport of the scalar second-order structure function ⟨(δq)2⟩. This calls into play componental third-order correlations ⟨(δq)2δu⟩(r) in axisymmetric turbulence. This permits to discuss inhomogeneous anisotropic effects from spatial decay, shear, or production, as in the central region of a rotating round jet. We show that the above-mentioned important statistical quantities can be estimated from experimental planar particle image velocimetry, and that explicit passage relations systematically exist between one- and two-point statistics in physical and spectral space for second-order tensors, but also sometimes for third-order tensors that are involved in the dynamics.

Photo-Induced Mass Transport in Thin Films of Amorphous As2S3

Abstract In this report direct photo-induced formation of surface relief gratings (SRG) in thin layers of arsenic sulfide (As 2 S 3 ) are shown. This anisotropic light-induced mass transfer phenomenon has been discussed with the special attention focused on the polarization and intensity of the corresponding light. The experimental setup for the SRG recording is straight-forward consisting of ~10 μm optical slit through which an unfocused beam of light is projected on the surface of sample. The evolution of surface relief in dependence from the recording time and polarization has been investigated in detail. The processes of SRG formation and mass transfer which are based on the photo-induced plasticity have discussed.

Tunable 2-μm optical vortex parametric oscillator

We generated tunable 2-μm optical vortex pulses with a topological charge of 1 or 2 in the wavelength range 1.953-2.158 μm by realizing anisotropic transfer of the topological charge from the pump beam to the signal output in a vortex-pumped half-symmetric optical parametric oscillator. A maximum vortex output energy of 2.1 mJ was obtained at a pump energy of 22.8 mJ, which corresponds to a slope efficiency of 15%. The topological charges of the signal and idler output were investigated using a shearing interferometric technique employing a low-spatial-frequency transmission grating.

Toward an accurate numerical simulation of radiation hydrodynamics in laser ablation plasmas

A radiation hydrodynamics code has been developed for more accurate prediction of laser-produced low-density ablation plasmas with appropriately describing anisotropic radiation field by using Monte-Carlo technique for variable Eddington tensor with reasonable computational loads. The Eddington tensor estimated by thousand of sample particles per single fluid step can reproduce the anisotropic radiation field in the low-density region and will not result in large computational consumption. Prediction of the emitted light from ablation plasma can be corrected by the proposed method. Ablation structure sustained by a compact radiation source, which is sometimes found in experiments of collisionless shock relevant to laboratory astrophysics, may also be changed by anisotropic transfer computation in optically thin region.

Theoretical study of the charge carrier mobilities of the molecular materials tetrathiafulvalene (TTF) and 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP)

Tetrathiafulvalene (TTF) is a kind of fused ring aromatic compound containing four sulfur atoms in one molecule, which is well known as a charge transport material. In order to calculate the charge mobility of this semiconductor, Marcus electron transfer theory and the embedded model, which can give small intramolecular reorganization energies, were employed. The calculated results were in good agreement with the experimental values, so the above computing model is appropriate to assess the electrical property of TTF. On this basis, we predicted the charge mobility of 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6- tetrathiapentalene (BDH-TTP) crystals, for which the molecular structure is similar to TTF. The calculated results indicated that BDH-TTP is a p-type material, which has a better performance than TTF in hole transfer due to larger hole coupling and the smaller hole injection barrier. In addition, the direct coupling (DC) and the site energy correction (SEC) methods were used to calculate the charge transfer integrals. Although the results were slightly different, the qualitative trends were the same. Furthermore we took into account the anisotropic transfer properties of TTF and BDH-TTF, since obviously the mobilities along one dimension are larger than those along three dimensions. Finally, natural bond orbital analysis was used to study the interactions in all of the dimers.

The impact of light polarization on the direct relief forming processes in As2S3 thin films

In this report direct a photo-induced formation of surface relief gratings (SRG) in thin layers of arsenic sulfide (As2S3) are shown. This anisotropic light-induced mass transfer phenomenon has been discussed with the special attention focused on the polarization and intensity of the corresponding light. The experimental setup for the SRG recording is straightforward consisting of ~10μm optical slit through which an unfocused beam of light is projected on the surface of sample. The verified sets of experimental parameters (light intensity, polarization and slit opening) were chosen. Additionally the evolution of surface relief in dependence from the recording time and polarization has been investigated in detail. The processes of SRG formation and mass transfer which are based on the photo-induced plasticity in As2S3 have been discussed.

Flux transport dynamo coupled with a fast tachocline scenario

AbstractThe tachocline is important in the solar dynamo for the generation and the storage of the magnetic fields. A most plausible explanation for the confinement of the tachocline is given by the fast tachocline model in which the tachocline is confined by the anisotropic momentum transfer by the Maxwell stress of the dynamo generated magnetic fields. We employ a flux transport dynamo model coupled with the simple feedback formula of this fast tachocline model which basically relates the thickness of the tachocline to the Maxwell stress. We find that this nonlinear coupling not only produces a stable solar-like dynamo solution but also a significant latitudinal variation in the tachocline thickness which is in agreement with the observations.