Comparison of terrain-based drift models to improve the quality of soil predictive mapping at a field scale

The ecological, economic, and agricultural benefits of accurate interpolation of spatial distribution patterns of soil properties are well recognized. In the present study different approaches to build the drift model for the regression kriging are analyzed and compared for estimating the spatial variation of humus and physical clay at soil depth (0-20 cm) in Tatarstan, Russian Federation. The soil sampling was performed according to an agrochemical sampling design: the field was divided into 60 sections; within each section 12-15 sampling points were taken using a hand auger at the depth of 10-20 cm to produce one mixed sample. Three terrain-based drift models: principal component regression (PCR), partial least squares (PLS), and random forest were used to predict the spatial distribution of humus and physical clay. Cross-validation was applied to evaluate the accuracy of interpolation methods through mean error (ME), root mean square error (RMSE), root mean square standardized error (RMSSE), and ratio of the observed and the predicted variances (RVar). The results indicate that ordinary kriging (OK) is superior when the data have strong spatial dependence. But in other cases, the PLS approach had the best prediction performance

Method for reliable realization of a varphi Josephson junction

We propose a method to realize a $\phi$ Josephson junction by combining alternating 0 and $\pi$ parts (sub junctions) with an intrinsically non-sinusoidal current-phase relation (CPR). Conditions for the realization of the $\phi$ ground state are analyzed. It is shown that taking into account the non-sinusoidal CPR for a "clean junction with a ferromagnetic (F) barrier, one can significantly enlarge the domain (regime of suitable F-layer thicknesses) of the $\phi$ ground state and make the practical realization of $\phi$ Josephson junctions feasible. Such junctions may also have two different stable solutions, such as 0 and $\pi$, 0 and $\phi$, or $\phi$ and $\pi$

Antiferromagnetic resonances in superconductor-ferromagnet multilayers

In this work, we study magnetization dynamics in superconductor-ferromagnet (S-F) thin-film multilayer. Theoretical considerations supported by the broad-band ferromagnetic resonance spectroscopy reveal development of acoustic and optic resonance modes in S-F multilayers at significantly higher frequencies in comparison to the Kittel mode of individual F-layers. These modes are formed due to antiferromagnetic-like interaction between F-layers via shared circulating superconducting currents in S-layers. The gap between resonance modes is determined by the thickness and superconducting penetration depth in S-layers. Overall, rich spectrum of S-F multilayers and its tunability opens wide prospects for application of these multialyers in magnonics as well as in various superconducting hybrid systems.Comment: 5 pages, 4 figures, 34 reference

Two-dimensional Ising model with competing interactions and its application to clusters and arrays of π\pi-rings and adiabatic quantum computing

We study planar clusters consisting of loops including a Josephson $\pi$-junction ($\pi$-rings). Each $\pi$-ring carries a persistent current and behaves as a classical orbital moment. The type of particular state associated with the orientation of orbital moments at the cluster depends on the interaction between these orbital moments and can be easily controlled, i.e. by a bias current or by other means. We show that these systems can be described by the two-dimensional Ising model with competing nearest-neighbor and diagonal interactions and investigate the phase diagram of this model. The characteristic features of the model are analyzed based on the exact solutions for small clusters such as a 5-site square plaquette as well as on a mean-field type approach for the infinite square lattice of Ising spins. The results are compared with spin patterns obtained by Monte Carlo simulations for the 100 $\times$ 100 square lattice and with experiment. We show that the $\pi$-ring clusters may be used as a new type of superconducting memory elements. The obtained results may be verified in experiments and are applicable to adiabatic quantum computing where the states are switched adiabatically with the slow change of coupling constants.Comment: 32 pages, 22 figures, RevTe

Theory of doorway states for one-nucleon transfer reactions. II. Model-independent study of nuclear correlation effects

The correlation effects in nuclei owing to which the nuclear wave functions are different from the Slater determinants are studied on the basis of the original theory. The calculated numbers of nucleons out of the nuclear Fermi-surface are in reasonable agreement with the finding from the high-momentum components of the nucleon momentum distributions in nuclei. The problems concerning the nuclear binding energy are also discussed.Comment: 11 pages LaTeX, epsfig.sty + 1 PostScript figure. submitted to Journal of Nuclear Physic

Evidence for two-dimensional nucleation of superconductivity in MgB2_{2}

According to the crystal structure of MgB$_{2}$ and band structure calculations quasi-two-dimensional (2D) boron planes are responsible for the superconductivity. We report on critical fields and resistance measurements of 30 nm thick MgB$_{2}$ films grown on MgO single crystalline substrate. A linear temperature dependence of the parallel and perpendicular upper critical fields indicate a 3D-like penetration of magnetic field into the sample. Resistivity measurements, in contrast, yield a temperature dependence of fluctuation conductivity above T$_{c}$ which agrees with the Aslamazov-Larkin theory of fluctuations in 2D superconductors. We consider this finding as an experimental evidence of two-dimensional nucleation of superconductivity in MgB$_{2}$.Comment: 5 RevTex pages, 3 PostScript Figures ZIPed in archive Sidoren.zip. Submitted to EuroPhys. Lett. December 3, 200

Re-entrant superconductivity in Nb/Cu(1-x)Ni(x) bilayers

We report on the first observation of a pronounced re-entrant superconductivity phenomenon in superconductor/ferromagnetic layered systems. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu(1-x)Ni(x). The superconducting transition temperature T_{c} drops sharply with increasing thickness d_{CuNi} of the ferromagnetic layer, until complete suppression of superconductivity is observed at d_{CuNi}= 4 nm. Increasing the Cu(1-x)Ni(x) layer thickness further, superconductivity reappears at d_{CuNi}=13 nm. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one dimensional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state in the ferromagnetic layer.Comment: 3 pages, 3 figures, REVTEX4/twocolum