Impact of the various spin and orbital ordering processes on multiferroic properties of orthovanadate DyVO3

The orthovanadate DyVO3 crystal, known to exhibit multiple structural, spin and orbital ordering transitions, is presently investigated on the basis of magnetization, heat capacity, resistivity, dielectric and polarization measurements. Our main result is experimental evidence for the existence of multiferroicity below a high TC of 108 K over a wide temperature range including different spin-orbital ordered states. The onset of ferroelectricity is found to coincide with the antiferromagnetic C-type spin ordering transition taking place at 108 K, which indicates that DyVO3 belongs to type II multiferroics exhibiting a coupling between magnetism and ferroelectricity. Some anomalies detected on the temperature dependence of electric polarization are discussed with respect to the nature of the spin-orbital ordered states of the V sublattice and the degree of spin alignment in the Dy sublattice. The orthovanadates RVO3 (R = rare earth or Y) form an important new category for searching for high-TC multiferroics.Comment: 25 pages, 7 figures, 68 references, one supplementary material, Physical Review B, Published 23 July 201

Magnetic anisotropy and spin-spiral wave in V, Cr and Mn atomic chains on Cu(001) surface: First principles calculations

Recent ab intio studies of the magnetic properties of all 3d transition metal(TM) freestanding atomic chains predicted that these nanowires could have a giant magnetic anisotropy energy (MAE) and might support a spin-spiral structure, thereby suggesting that these nanowires would have technological applicationsin, e.g., high density magnetic data storages. In order to investigate how the substrates may affect the magnetic properties of the nanowires, here we systematically study the V, Cr and Mn linear atomic chains on the Cu(001) surface based on the density functional theory with the generalized gradient approximation. We find that V, Cr, and Mn linear chains on the Cu(001) surface still have a stable or metastable ferromagnetic state. However, the ferromagnetic state is unstable against formation of a noncollinear spin-spiral structure in the Mn linear chains and also the V linear chain on the atop sites on the Cu(001) surface, due to the frustrated magnetic interactions in these systems. Nonetheless, the presence of the Cu(001) substrate does destabilize the spin-spiral state already present in the freestanding V linear chain and stabilizes the ferromagnetic state in the V linear chain on the hollow sites on Cu(001). When spin-orbit coupling (SOC) is included, the spin magnetic moments remain almost unchanged, due to the weakness of SOC in 3d TM chains. Furthermore, both the orbital magnetic moments and MAEs for the V, Cr and Mn are small, in comparison with both the corresponding freestanding nanowires and also the Fe, Co and Ni linear chains on the Cu (001) surface.Comment: Accepted for publication in J. Phys. D: Applied Physic

Optimal Topological Test for Degeneracies of Real Hamiltonians

We consider adiabatic transport of eigenstates of real Hamiltonians around loops in parameter space. It is demonstrated that loops that map to nontrivial loops in the space of eigenbases must encircle degeneracies. Examples from Jahn-Teller theory are presented to illustrate the test. We show furthermore that the proposed test is optimal.Comment: Minor corrections, accepted in Phys. Rev. Let

Suppression of dynamic stall with a leading-edge slat on a VR-7 airfoil

The VR-7 airfoil was experimentally studied with and without a leading-edge slat at fixed angles of attack from 0 deg to 30 deg at Re = 200,000 and for unsteady pitching motions described by alpha equals alpha(sub m) + 10 deg(sin(wt)). The models were two dimensional, and the test was performed in a water tunnel at Ames Research Center. The unsteady conditions ranged over Re equals 100,000 to 250,000, k equals 0.001 to 0.2, and alpha(sub m) = 10 deg to 20 deg. Unsteady lift, drag, and pitching-moment measurements were obtained along with fluorescent-dye flow visualizations. The addition of the slat was found to delay the static-drag and static-moment stall by about 5 degrees and to eliminate completely the development of a dynamic-stall vortex during unsteady motions that reached angles as high as 25 degrees. In all of the unsteady cases studied, the slat caused a significant reduction in the force and moment hysteresis amplitudes. The reduced frequency was found to have the greatest effect on the results, whereas the Reynolds number had little effect on the behavior of either the basic or the slatted airfoil. The slat caused a slight drag penalty at low angles of attack, but generally increased the lift/drag ratio when averaged over the full cycle of oscillation

Airfoil interaction with impinging vortex

The tip of a finite-span airfoil was used to generate a streamwise vortical flow, the strength of which could be varied by changing the incidence of the airfoil. The vortex that was generated traveled downstream and interacted with a second airfoil on which measurements of lift, drag, and pitching moment were made. The flow field, including the vortex core, was visualized in order to study the structural alterations to the vortex resulting from various levels of encounter with the downstream airfoil. These observations were also used to evaluate the accuracy of a theoretical model

Resonant Subband Landau Level Coupling in Symmetric Quantum Well

Subband structure and depolarization shifts in an ultra-high mobility GaAs/Al_{0.24}Ga_{0.76}As quantum well are studied using magneto-infrared spectroscopy via resonant subband Landau level coupling. Resonant couplings between the 1st and up to the 4th subbands are identified by well-separated anti-level-crossing split resonance, while the hy-lying subbands were identified by the cyclotron resonance linewidth broadening in the literature. In addition, a forbidden intersubband transition (1st to 3rd) has been observed. With the precise determination of the subband structure, we find that the depolarization shift can be well described by the semiclassical slab plasma model, and the possible origins for the forbidden transition are discussed.Comment: 4 pages, 2 figure

Heavy Quark Mass Effects in Deep Inelastic Scattering and Global QCD Analysis

A new implementation of the general PQCD formalism of Collins, including heavy quark mass effects, is described. Important features that contribute to the accuracy and efficiency of the calculation of both neutral current (NC) and charged current (CC) processess are explicitly discussed. This new implementation is applied to the global analysis of the full HERA I data sets on NC and CC cross sections, with correlated systematic errors, in conjunction with the usual fixed-target and hadron collider data sets. By using a variety of parametrizations to explore the parton parameter space, robust new parton distribution function (PDF) sets (CTEQ6.5) are obtained. The new quark distributions are consistently higher in the region x ~ 10^{-3} than previous ones, with important implications on hadron collider phenomenology, especially at the LHC. The uncertainties of the parton distributions are reassessed and are compared to the previous ones. A new set of CTEQ6.5 eigenvector PDFs that encapsulates these uncertainties is also presented.Comment: 32 pages, 12 figures; updated, Publication Versio

How should one formulate, extract, and interpret `non-observables' for nuclei?

Nuclear observables such as binding energies and cross sections can be directly measured. Other physically useful quantities, such as spectroscopic factors, are related to measured quantities by a convolution whose decomposition is not unique. Can a framework for these nuclear structure `non-observables' be formulated systematically so that they can be extracted from experiment with known uncertainties and calculated with consistent theory? Parton distribution functions in hadrons serve as an illustrative example of how this can be done. A systematic framework is also needed to address questions of interpretation, such as whether short-range correlations are important for nuclear structure.Comment: 7 pages. Contribution to the "Focus issue on Open Problems in Nuclear Structure", Journal of Physics

Effect of an extendable slat on the stall behavior of a VR-12 airfoil

Experimental and computational tests were performed on a VR-12 airfoil to determine if the dynamic-stall behavior that normally accompanies high-angle pitch oscillations could be modified by segmenting the forward portion of the airfoil and extending it ahead of the main element. In the extended position the configuration would appear as an airfoil with a leading-edge slat, and in the retracted position it would appear as a conventional VR-12 airfoil. The calculations were obtained from a numerical code that models the vorticity transport equation for an incompressible fluid. These results were compared with test data from the water tunnel facility of the Aeroflightdynamics Directorate at Ames Research Center. Steady and unsteady flows around both airfoils were examined at angles of attack between 0 and 30 deg. The Reynolds number was fixed at 200,000 and the unsteady pitch oscillations followed a sinusoidal motion described by alpha = alpha(sub m) + 10 deg sin(omega t). The mean angle (alpha(sub m)) was varied from 10 to 20 deg and the reduced frequency from 0.05 to 0.20. The results from the experiment and the calculations show that the extended-slat VR-12 airfoil experiences a delay in both static and dynamic stall not experienced by the basic VR-12 airfoil

Quantum Number Density Asymmetries Within QCD Jets Correlated With Lambda Polarization

The observation of jets in a variety of hard-scattering processes has allowed the quantitative study of perturbative quantum chromodynamics (PQCD) by comparing detailed theoretical predictions with a wide range of experimental data. This paper examines how some important, nonperturbative, facets of QCD involving the internal dynamical structure of jets can be studied by measuring the spin orientation of Lambda particles produced in these jets. The measurement of the transverse polarization for an individual Lambda within a QCD jet permits the definition of spin-directed asymmetries in local quantum number densities in rapidity space (such as charge, strangeness and baryon number densities) involving neighboring hadrons in the jet. These asymmetries can only be generated by soft, nonperturbative dynamical mechanisms and such measurements can provide insight not otherwise accessible into the color rearrangement that occurs during the hadronization stage of the fragmentation process.Comment: The replacement manuscript contains a new abstract, five pages of additional material and a revised version of Fig.