Anisotropy In Space Research Articles

ON THE ANISOTROPIC NATURE OF MRI-DRIVEN TURBULENCE IN ASTROPHYSICAL DISKS

The magnetorotational instability is thought to play an important role in enabling accretion in sufficiently ionized astrophysical disks. The rate at which MRI-driven turbulence transports angular momentum is related to both the strength of the amplitudes of the fluctuations on various scales and the degree of anisotropy of the underlying turbulence. This has motivated several studies of the distribution of turbulent power in spectral space. In this paper, we investigate the anisotropic nature of MRI-driven turbulence using a pseudo-spectral code and introduce novel ways to robustly characterize the underlying turbulence. We show that the general flow properties vary in a quasi-periodic way on timescales comparable to 10 inverse angular frequencies motivating the temporal analysis of its anisotropy. We introduce a 3D tensor invariant analysis to quantify and classify the evolution of the anisotropic turbulent flow. This analysis shows a continuous high level of anisotropy, with brief sporadic transitions towards two- and three-component isotropic turbulent flow. This temporal-dependent anisotropy renders standard shell-average, especially when used simultaneously with long temporal averages, inadequate for characterizing MRI-driven turbulence. We propose an alternative way to extract spectral information from the turbulent magnetized flow, whose anisotropic character depends strongly on time. This consists of stacking 1D Fourier spectra along three orthogonal directions that exhibit maximum anisotropy in Fourier space. The resulting averaged spectra show that the power along each of the three independent directions differs by several orders of magnitude over most scales, except the largest ones. Our results suggest that a first-principles theory to describe fully developed MRI-driven turbulence will likely have to consider the anisotropic nature of the flow at a fundamental level.

Use of precisely sculptured thin film (STF) substrates with generalized ellipsometry to determine spatial distribution of adsorbed fibronectin to nanostructured columnar topographies and effect on cell adhesion

Sculptured thin film (STF) substrates consist of nanocolumns with precise orientation, intercolumnar spacing, and optical anisotropy, which can be used as model biomaterial substrates to study the effect of homogenous nanotopogrophies on the three-dimensional distribution of adsorbed proteins. Generalized ellipsometry was used to discriminate between the distributions of adsorbed FN either on top of or within the intercolumnar void spaces of STFs, afforded by the optical properties of these precisely crafted substrates. Generalized ellipsometry indicated that STFs with vertical nanocolumns enhanced total FN adsorption two-fold relative to flat control substrates and the FN adsorption studies demonstrate different STF characteristics influence the degree of FN immobilization both on top and within intercolumnar spaces, with increasing spacing and surface area enhancing total protein adsorption. Mouse fibroblasts or mouse mesenchymal stem cells were subsequently cultured on STFs, to investigate the effect of highly ordered and defined nanotopographies on cell adhesion, spreading, and proliferation. All STF nanotopographies investigated in the absence of adsorbed FN were found to significantly enhance cell adhesion relative to flat substrates; and the addition of FN to STFs was found to have cell-dependent effects on enhancing cell–material interactions. Furthermore, the amount of FN adsorbed to the STFs did not correlate with comparative enhancements of cell–material interactions, suggesting that nanotopography predominantly contributes to the biocompatibility of homogenous nanocolumnar surfaces. This is the first study to correlate precisely defined nanostructured features with protein distribution and cell–nanomaterial interactions. STFs demonstrate immense potential as biomaterial surfaces for applications in tissue engineering, drug delivery, and biosensing.

Variations in the Anisotropy and Affine Structure of Visual Space: A Geometry of Visibles with a Third Dimension

A meta-analysis and an experiment show that the degree of compression of the in-depth dimension of visual space relative to the frontal dimension increases quickly as a function of the distance between the stimulus and the observer at first, but the rate of change slows beyond 7 m from the observer, reaching an apparent asymptote of about 50 %. In addition, the compression of visual space is greater for monocular and reduced cue conditions. The pattern of compression of the in-depth dimension as a function of distance is similar to the ratio of in-depth to frontal visual angles of stimuli, but is not as extreme as this ratio would suggest, implying that observers are incapable of fully ignoring size information provided by cues to depth. Size and distance judgments may be described by an Affine transformation of physical space; however, the compression parameter in this model changes as a function of distance from the observer and other experimental conditions.

The Quantum Effects Role on Weibel Instability Growth Rate in Dense Plasma

The Weibel instability is one of the basic plasma instabilities that plays an important role in stopping the hot electrons and energy deposition mechanism. In this paper, combined effect of the density gradient and quantum effects on Weibel instability growth rate is investigated. The results have shown that, by increasing the quantum parameter, for large wavelengths, the Weibel instability growth rate shrinks to zero. In the large wavelengths limit, the analysis shows that quantum effects and density gradient tend to stabilize the Weibel instability. The density perturbations have decreased the growth rate of Weibel instability in the near corona fuel,η>0.1. In the small wavelengths limit, for the density gradient,η<0.1, the tunneling quantum effects increase anisotropy in the phase space. The quantum tunneling effect leads to an unexpected increase in the Weibel instability growth rate.

First measurements of D(α) spectrum produced by anisotropic fast ions in the gas dynamic trap.

Angled injection of eight deuterium beams in gas dynamic trap (GDT) plasmas builds up the population of fast ions with the distribution function, which conserves a high degree of initial anisotropy in space, energy, and pitch angle. Unlike the Maxwellian distribution case, the fast ion plasma component in GDT cannot be exhaustively characterized by the temperature and density. The instrumentation complex to study of fast ions is comprised of motional Stark effect diagnostic, analyzers of charge exchange atoms, and others. The set of numerical codes using for equilibrium modeling is also an important tool of analysis. In the recent campaign of summer 2014, we recorded first signals from the new fast ion D-alpha diagnostic on GDT. This paper presents the diagnostic description and results of pilot measurements. The diagnostic has four lines of sight, distributed across the radius of an axially symmetric plasma column in GDT. In the present setup, a line-integrated optical signal is measured in each channel. In the transverse direction, the spatial resolution is 18 mm. Collected light comes to the grating spectrometer with the low-noise detector based on a charge-coupled device matrix. In the regime of four spectra stacked vertically on the sensor, the effective spectral resolution of measurements is approximately 0.015 nm. Exposure timing is provided by the fast optical ferroelectric crystal shutter, allowing frames of duration down to 70 μs. This number represents the time resolution of measurements. A large dynamic range of the camera permits for a measurement of relatively small light signals produced by fast ions on top of the bright background emission from the bulk plasma. The fast ion emission has a non-Gaussian spectrum featuring the characteristic width of approximately 4 nm, which can be separated from relatively narrow Gaussian lines of D-alpha and H-alpha coming from the plasma periphery, and diagnostic beam emission. The signal to noise ratio varies from approximately ten for the central channel to approximately five for the outermost channel. We used the special set of Monte Carlo codes to fit the measured spectra. The shape of model fit shows a good agreement with the experimental fast ion D-alpha spectrum.

Zeroing in on the initial state — tomography using bulk, jets and photons

One of the unsolved problems in the current 'standard model' of heavy ion physics is the apparent rapid thermalization of QCD matter in the pre-equilibrium stage. While it is challenging to probe this mechanism directly, there are now several observables available which allow tomographic imaging of the initial state geometry, which is expected to carry remnant information of the equilibration mechanism. On the fluid dynamics side, scaled fluctuations in the momentum space anisotropy parameters v_n image the initial eccentricity fluctuations epsilon_n almost directly with only a weak dependence on the details of the fluid dynamical evolution. From a different direction, due to the strong non-linear dependence of their emission rates on temperature, thermal photons and their v_n are very sensitive to the initial state graininess. Finally, the v_2 and v_3 of high P_T hadrons coming from hard processes reflect the attenuation pattern of partons propagating through the inhomogeneous matter density after some fluid dynamical evolution. Combining information from all these channels does not yet lead to a fully consistent picture, however intriguing trends pointing towards non-trivial initial state dynamics emerge.

Fine structure of the incommensurate antiferromagnetic fluctuations in single-crystalline LiFeAs studied by inelastic neutron scattering

We present an inelastic neutron scattering study on single-crystalline LiFeAs devoted to the characterization of the incommensurate antiferromagnetic fluctuations at $\mathbf{Q}=(0.5\pm\delta, 0.5\mp\delta, q_l)$. Time-of-flight measurements show the presence of these magnetic fluctuations up to an energy transfer of 60 meV, while polarized neutrons in combination with longitudinal polarization analysis on a triple-axis spectrometer prove the pure magnetic origin of this signal. The normalization of the magnetic scattering to an absolute scale yields that magnetic fluctuations in LiFeAs are by a factor eight weaker than the resonance signal in nearly optimally Co-doped BaFe$_2$As$_2$, although a factor two is recovered due to the split peaks owing to the incommensurability. The longitudinal polarization analysis indicates weak spin space anisotropy with slightly stronger out-of-plane component between 6 and 12 meV. Furthermore, our data suggest a fine structure of the magnetic signal most likely arising from superposing nesting vectors.

Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap

Using two experimental techniques, we studied single crystals of the 122-FeAs family with almost the same critical temperature, Tc. We investigated the temperature dependence of the lower critical field of a single crystal under static magnetic fields parallel to the axis. The temperature dependence of the London penetration depth can be described equally well either by a single anisotropic -wave-like gap or by a two-gap model, while a d-wave approach cannot be used to fit the London penetration depth data. Intrinsic multiple Andreev reflection effect spectroscopy was used to detect bulk gap values in single crystals of the intimate compound, with the same Tc. We estimated the range of the large gap value 6-8 meV (depending on small variation of and its a space anisotropy of about 30%, and the small gap 1.7 meV. This clearly indicates that the gap structure of our investigated systems more likely corresponds to a nodeless s-wave two gaps.

Spin-Flop Phenomenon of Two-Dimensional Frustrated Antiferromagnets without Anisotropy in Spin Space

Motivated by a recent finding of a spin-flop phenomenon in a system without anisotropy in spin space reported in the S=1/2 Heisenberg antiferromagnet on the square-kagome lattice, we study the S=1/2 Heisenberg antiferromagnets on two other lattices composed of vertex-sharing triangles by the numerical diagonalization method. One is a novel lattice including a shuriken shape with four teeth; the other is the kagome lattice with $\sqrt{3}\times\sqrt{3}$-structure distortion, which includes a shuriken shape with six teeth. We find in the magnetization processes of these systems that a magnetization jump accompanied by a spin-flop phenomenon occurs at the higher-field-side edge of the magnetization plateau at one-third the height of saturation. This finding indicates that the spin-flop phenomenon found in the isotropic system on the square-kagome lattice is not an exceptional case.

Constraints fromv2fluctuations for the initial-state geometry of heavy-ion collisions

The ability to accurately compute the series of coefficients $v_n$ characterizing the momentum space anisotropies of particle production in ultrarelativistic heavy ion collisions as a function of centrality is widely regarded as a triumph of fluid dynamics as description of the bulk matter evolution. A key ingredient to fluid dynamical modeling is however the initial spatial distribution of matter as created by a yet not completely understood equilibration process. A measurement directly sensitive to this initial state geometry is therefore of high value for constraining models of pre-equilibrium dynamics. Recently, it has been shown that such a measurement is indeed possible in terms of the event by event probability distribution of the normalized $v_n$ distribution as a function of centrality, which is to high accuracy independent on the details of the subsequent fluid dynamical evolution and hence directly reflects the primary distribution of spatial eccentricities. We present a study of this observable using a variety of Glauber-based models and argue that the experimental data place very tight constraints on the initial distribution of matter and rule out all simple Glauber-based models.

Two-photon correlation in anisotropic quark-gluon plasma

The only way to obtain the space-time structure of heavy ion collision is through the study of two-particle momentum correlations. Thus we have studied the intensity correlation for the photons having fixed transverse momentum of one of the photons ($k_{1T}$= 2 GeV) in anisotropic Quark Gluon Plasma (aQGP) to have an idea about emission zone in presence of initial momentum anisotropy. The {\em free streaming interpolating} model with fixed initial condition has been used for the space-time evolution for most central collision at RHIC energy. The variation of Bose-Einstein correlation function (BECF), $C_2$, for two identical photons as a function of $q_{out}$, $q_{side}$ and $q_{long}$ is evaluated. We have restricted our analysis only to QGP phase to know the effect of anisotropy on the correlation function and HBT radii extracted. It is observed that the longitudinal dimension of the reaction zone is mostly affected due to the presence of momentum space anisotropy.

Momentum space anisotropy of electronic correlations in Fe and Ni: An analysis of magnetic Compton profiles

The total and magnetically resolved Compton profiles are analyzed within the combined density functional and dynamical mean field theory for the transition metal elements Fe and Ni. A rather good agreement between the measured and computed magnetic Compton profiles (MCPs) of Fe and Ni is obtained with the standard Local Spin Density Approximation (LSDA). By including local but dynamic many-body correlations captured by Dynamical Mean Field Theory (DMFT), the calculated magnetic Compton profile is further improved when compared with experiment. The second moment of the difference of the total Compton profiles between LSDA and DMFT, along the same momentum direction, has been used to discuss the strength of electronic correlations in Fe and Ni.

Multi-level modelling of mechanical anisotropy of commercial pure aluminium plate: Crystal plasticity models, advanced yield functions and parameter identification

The mechanical anisotropy of an AA1050 aluminium plate is studied by the use of five crystal plasticity models and two advanced yield functions. In-plane uniaxial tension properties of the plate were predicted by the full-constraint Taylor model, the advanced Lamel model (Van Houtte et al., 2005) and a modified version of this model (Mánik and Holmedal, 2013), the viscoplastic self-consistent model and a crystal plasticity finite element method (CPFEM). Results are compared with data from tensile tests at every 15° from the rolling direction (RD) to the transverse direction (TD) in the plate. Furthermore, all the models, except CPFEM, were used to provide stress points in the five-dimensional deviatoric stress space at yielding for 201 plastic strain-rate directions. The Facet yield surface was calibrated using these 201 stress points and compared to in-plane yield loci and the planar anisotropy which were calculated by the crystal plasticity models. The anisotropic yield function Yld2004-18p (Barlat et al., 2005) was calibrated by three methods: using uniaxial tension data, using the 201 virtual yield points in stress space, and using a combination of experimental data and virtual yield points (i.e. a hybrid method). Optimal yield-surface exponents were found for each of the crystal plasticity models, based on calibration to calculated stress points at yielding for a random texture, and used in the latter two calibration methods. It is found that the last hybrid calibration method can capture the experimental results and at the same time ensure a good fit to the anisotropy in the full stress space predicted by the crystal plasticity models.

Tornadoes and the Global Anisotropy of the Physical Space

Whereas the basic physical mechanisms leading to the onset and evolution of tornadoes have been well established, some progress can still be useful to identify the conditions supporting the development of a tornado towards a violent or catastrophic stage, as well as possible specific and observable events triggering the onset of a tornado in a generally favorable atmospheric environment. On the basis of an assumed global anisotropy of the physical spaceand the associated non-gauge byuon theory, an additional mechanism of energy accumulation in the process of development of a tornado to its mature stage is proposedand its consistency is checked against a dataset of individual tornadoes as well as of tornado outbreaks. The results point to a significant link between the angle formed by the cosmological vector potentialrepresenting the global anisotropy of the physical space and the surface tangent to the local Earth’s surface and the occurrence of the most energetic tornadoes; as a consequence, such tornadoes are shown to occur only at specific times of the day depending on latitude, longitude and day of the year. Moreover, a further additional mechanism is proposed for the early origin of a tornado, on the basis of the interaction of a large peak current lightning discharge with the cosmological vector potential introduced by the byuon theory. It is shown how, in the framework of the proposed theory, a fraction of the energy of a tornado at its onset stage can originate from the self-energy associated with the formation of the physical space of elementary particles located along the lightning discharge. The verification of the proposed mechanism for the onset of tornadoes is delayed to later time when suitable data sets will be available.

New Force, Global Anisotropy and the Changes in β-Decay Rate of Radioactive Elements

The review of experimental studies results of a global anisotropy of physical space and new interaction in nature based on analyzing fluctuations in the intensity of the β-decay of radioactive elements are presented. The explanation of the results, based on a hypothesis as to the global anisotropy of physical space caused by the existence of cosmological vector potential AG in limits of theory of byuon, is given. It is shown that vector AG has the following coordinates in the second equatorial coordinate system: right ascension α = 293° ± 15°; declination δ = 36° ± 10°.

New Spacecraft and Protection of the Planet from the Asteroid Hazard

A project is presented to create in Mars’ orbit a protective stations belt (PSB) designed to bring down the asteroid hazard to the Earth, based on an interplanetary spacecraft(ISC) of a new type. This project may as well contribute to the investigation of fundamental problems of astronomy and astrophysics in the study of the properties of deep space using space platforms. The project is based on technical realizations which feasibility derives from the cosmological theory of byuon (TB) about the formation of the physical space and the world of elementary particles along with the experimental findings about new properties of nature: a new force that is used in the form of thrust for spacecrafts and a new quantum information channel providing a connection between the Earth, the PSB and the ISC. The results of experimental investigations about the traction force with a ground model of spacecraft are recalled, confirming the existence of a global anisotropy of physical space as predicted by the theory of byuon, as well as the technical feasibility to harness the new force in order to implement new concept space thrusters significantly more energy-effective than existing models. An action plan to implement the creation of the ISC is worked out.

Experimental Investigation of the Traction Force for a New Space Thruster

A long course of experimental investigations of a new non-gauge force used for the traction of a prototype space thruster placed on board an hemispherical ship are reviewed and discussed. The physical nature of the new force is explained by the theory of byuon, a non-gauge theory of the formation of the physical space and the world of ultimate particles from some unobservable objects called “byuons”. The definition of these objects contains a new fundamental vector constant, the cosmological vector potential Ag, which direction defines a marginal global anisotropy of the physical space. The experimental results show a remarkable dependence of the force on the period of the year and even on the time of the day, the details of such dependence suggesting astronomical coordinates of the vector Ag which are consistent with previous estimates yet reducing their uncertainty: in the second equatorial coordinates system, the right ascension α=316°±5° and the declination δ=36°±10° are obtained. The level of the traction force during the experimental period turns out to be in the range 2.5 mN to 51 mN, while the best figure for the power to thrust ratio as derived from previous experiments is 330 W/N, suggestive of its potential competitiveness with state of the art electric propulsion thrusters.

A New Additional Energy Source for Tornadoes

Following earlier research aimed at detecting evidence of a connection between selected very powerful tornadoes and the global anisotropy of the physical space representing the foundation of the theory of byuons, allegedly realized by means of a positive feedback between the tornado updraft and the cosmological vector representing the global anisotropy, this article extends the analysis to a much larger database of tornadic events occurring in the continental U.S. in order to detect the fingerprint of the new proposed physical processes on the overall statistics. While the theoretical foundations of the onset and development of tornadoes are well established, some work remains to be done with particular reference to the upper tail of the energy distribution of tornadoes, where the energy developed by a single event can be as huge as 1016 J, or the equivalent of 2 Mton of TNT. In this range, additional mechanisms of energy supply in the process of development of a tornado are proposed and their fingerprint on the overall statistics are looked for. Although further analyses over different geographical areas, especially in the southern hemisphere, would be needed in order to provide a really conclusive proof, convincing evidence accumulates and points to the reality of the new proposed physical processes.

Independence of egocentric and exocentric direction processing in visual space.

major issue concerning investigations of visual perception is determination of the geometrical properties of visual space. To address this issue, one must determine the relationships between geometrical features of visual space, distance, direction, angle, and size. Consistent evidence indicates that visual angle is a determinant of perceived exocentric distance. Previous evidence suggests that exocentric distance and direction are hierarchically processed, with distance preceding direction. The present study investigated the relationship between the perceptual processing of egocentric direction and exocentric direction using a task that independently provides both perceptual variables in a single judgment. The results indicated that egocentric directions were systematically overestimated, and this was not caused by either the global shape of the layout or leg length effects. Exocentric directions presented a discontinuous pattern of overestimation of smaller angles that were subtended by radial orientations and accuracy of right angles that were subtended by horizontal orientations. This could be explained by the anisotropy of visual space, a well-established phenomenon from visual space studies. The analysis of the association between the processing of these two variables revealed independence between them in which exocentric direction processing did not depend on the processing of egocentric direction processing, and vice versa. The present results and prior evidence converge on the notion of hierarchical processing in which the visual system processes the egocentric distance of objects followed by exocentric distance processing and subsequent processing. The precise positions of egocentric and exocentric directions in this chain of processing remain to be determined. Keywords: visual space perception, exocentric direction, egocentric direction, angle perception.

Global Anisotropy and Theory of Byuon

The basic ideas of an unconventional physical model of creation of the observed physical space and ultimate particles from a finite set of special discrete objects (byuons) are presented and discussed. The qualitative distinctions between the theory of byuons and previous physical theories are discussed. Predictions of theory of byuons are proposed: the existence of the cosmological vectorial potential Ag, a novel fundamental vectorial constant defining the global anisotropy of physical space, a new force of nature and the quantum information channel.