A geometric Newton method for Oja's vector field

Newton's method for solving the matrix equation $F(X)\equiv AX-XX^TAX=0$ runs up against the fact that its zeros are not isolated. This is due to a symmetry of $F$ by the action of the orthogonal group. We show how differential-geometric techniques can be exploited to remove this symmetry and obtain a ``geometric'' Newton algorithm that finds the zeros of $F$. The geometric Newton method does not suffer from the degeneracy issue that stands in the way of the original Newton method

Modeling charge-imbalanced NaNbO3/SrTiO3 superlattices: Lattice relaxation and metallicity

The electronic and structural properties of different charge-imbalanced perovskite oxide NaNbO3/SrTiO3 superlattices are investigated with density-functional theory (local density approximation and local spin density approximation+U) methods. Metallic or insulating behavior of such a superlattice depends on the types of interfaces present: nonstoichiometric composition of a superlattice introduces holes to O p orbitals or extra electrons to Nb/Ti d orbitals. Lattice parameters, superlattice volume, and the extent of conduction electron or hole states are found to depend on interface type. The extent of the metallic state may also depend on the NaNbO3/SrTiO3 ratio. Octahedral rotations and other low-symmetry phases increase the gap between p and d orbitals but do not affect metallicity. Adding a Hubbard U to account for possible electronic correlations does not affect electron localization. Within LSDA+U, the delocalized holes align ferromagnetically.Peer reviewe

d0 Ferromagnetic Interface Between Non-magnetic Perovskites

We use computational and experimental methods to study d0 ferromagnetism at a charge- imbalanced interface between two perovskites. In SrTiO3/KTaO3 superlattice calculations, the charge imbalance introduces holes in the SrTiO3 layer, inducing a d0 ferromagnetic half-metallic 2D electron gas at the interface oxygen 2p orbitals. The charge imbalance overrides doping by vacancies at realistic concentrations. Varying the constituent materials shows ferromagnetism to be a gen- eral property of hole-type d0 perovskite interfaces. Atomically sharp epitaxial d0 SrTiO3/KTaO3, SrTiO3 /KNbO3 and SrTiO3 /NaNbO3 interfaces are found to exhibit ferromagnetic hysteresis at room temperature. We suggest the behavior is due to high density of states and exchange coupling at the oxygen t1g band in comparison with the more studied d band t2g symmetry electron gas.Comment: 5 pages, 5 figure

Computational study of (111) epitaxially strained ferroelectric perovskites BaTiO3 and PbTiO3

The phase transition behavior of PbTiO3 and BaTiO3 under (111) epitaxial strain is investigated using density-functional theory calculations. From tensile strains of +0.015 to compressive strains of −0.015, PbTiO3 undergoes phase transitions from C2 through two Cm phases and then to R3m. The total polarization is found to be almost independent of strain. For the same range of strains BaTiO3 undergoes phase transitions from a single Cm phase, through R3m and then to R3¯m. In this case the application of compressive strain inhibits and then completely suppresses the polarization on transition to the nonpolar R3¯m phase.Peer reviewe

Tidying up international nucleotide sequence databases

Sequence analysis of the ribosomal RNA operon, particularly the internal transcribed spacer (ITS) region, provides a powerful tool for identification of mycorrhizal fungi. The sequence data deposited in the International Nucleotide Sequence Databases (INSD) are, however, unfiltered for quality and are often poorly annotated with metadata. To detect chimeric and low-quality sequences and assign the ectomycorrhizal fungi to phylogenetic lineages, fungal ITS sequences were downloaded from INSD, aligned within family-level groups, and examined through phylogenetic analyses and BLAST searches. By combining the fungal sequence database UNITE and the annotation and search tool PlutoF, we also added metadata from the literature to these accessions. Altogether 35,632 sequences belonged to mycorrhizal fungi or originated from ericoid and orchid mycorrhizal roots. Of these sequences, 677 were considered chimeric and 2,174 of low read quality. Information detailing country of collection, geographical coordinates, interacting taxon and isolation source were supplemented to cover 78.0%, 33.0%, 41.7% and 96.4% of the sequences, respectively. These annotated sequences are publicly available via UNITE (http://unite.ut.ee/) for downstream biogeographic, ecological and taxonomic analyses. In European Nucleotide Archive (ENA; http://www.ebi.ac.uk/ena/), the annotated sequences have a special link-out to UNITE. We intend to expand the data annotation to additional genes and all taxonomic groups and functional guilds of fungi

Evidence for Strain-Induced Ferroelectric Order in Epitaxial Thin-Film KTaO3

In perovskite-structure epitaxial films, it has been theoretically predicted that the polarization and the coherence of polar order can increase with increasing crystallographic strain. Experimental evidence of strain-induced long-range ferroelectric order has not been obtained thus far, posing the fundamental question of whether or not strain can induce the long-range polar order. Here we demonstrate the existence of strain-induced ferroelectric order in quantum paraelectric KTaO3 by combining experimental investigations of epitaxial KTaO3 films and density-functional-theory calculations. The long-range ferroelectric order does exist under a large enough epitaxial strain. We suggest that a region of short-range polar order might appear between paraelectric and ferroelectric states in the strain-temperature phase diagrams.Peer reviewe

Spectroscopic and Photometric Study of the Contact Binary BO CVn

We present the results of the study of the contact binary system BO CVn. We have obtained physical parameters of the components based on combined analysis of new, multi-color light curves and spectroscopic mass ratio. This is the first time the latter has been determined for this object. We derived the contact configuration for the system with a very high filling factor of about 88 percent. We were able to reproduce the observed light curve, namely the flat bottom of the secondary minimum, only if a third light has been added into the list of free parameters. The resulting third light contribution is significant, about 20-24 percent, while the absolute parameters of components are: M1=1.16, M2=0.39, R1=1.62 and R2=1.00 (in solar units). The O-C diagram shows an upward parabola which, under the conservative mass transfer assumption, would correspond to a mass transfer rate of dM/dt = 6.3 \times 10-8M\odot/yr, matter being transferred from the less massive component to the more massive one. No cyclic, short-period variations have been found in the O-C diagram (but longer-term variations remain a possibility)Comment: 16 pages, 5 figures, 5 tables, accepted for publication by New Astronom

Radial Velocity Studies of Close Binary Stars. IX

Radial-velocity measurements and sine-curve fits to the orbital velocity variations are presented for the eighth set of ten close binary systems: AB And, V402 Aur, V445 Cep, V2082 Cyg, BX Dra, V918 Her, V502 Oph, V1363 Ori, KP Peg, V335 Peg. Half of the systems (V445 Cep, V2082 Cyg, V918 Her, V1363 Ori, V335 Peg) were discovered photometrically by the Hipparcos mission and all systems are double-lined (SB2) contact binaries. The broadening function method permitted improvement of the orbital elements for AB And and V502 Oph. The other systems have been observed for radial velocity variations for the first time; in this group are five bright (V<7.5) binaries: V445 Cep, V2082 Cyg, V918 Her, KP Peg and V335 Peg. Several of the studied systems are prime candidates for combined light and radial-velocity synthesis solutions.Comment: 17+ pages, 2 tables, 4 figure

How well do physical activity questions perform? A European cognitive testing study

&lt;p&gt;&lt;b&gt;BACKGROUND: &lt;/b&gt;Only few studies have focused on the cognitive processes of the respondents that are involved when answering physical activity questionnaires (PAQs). This study aimed at examining whether two PAQs work as intended with different segments of the survey population in different cultural settings in Europe.&lt;/p&gt;&lt;p&gt;&lt;b&gt;METHODS: &lt;/b&gt;The International Physical Activity Questionnaire - Short Form (IPAQ-SF) and the US National Health Interview Survey - Adult Core Physical Activity Questionnaire (NHIS-PAQ) were tested in Belgium, Estonia, Germany and the UK using a standardized cognitive interviewing procedure. IPAQ-SF measures total vigorous physical activity (PA), moderate PA, walking and sitting. NHIS-PAQ measures leisure-time vigorous PA, light and moderate PA and muscle-strengthening PA. In total 62 persons completed cognitive interviews, at least 15 interviews were conducted in each country.&lt;/p&gt;&lt;p&gt;&lt;b&gt;RESULTS: &lt;/b&gt;Both PAQs performed as intended with young and high-skilled persons and those having a regular exercise schedule. For the others, however, the testing revealed that problems occurred with both PAQs relating to understanding the concepts of &#039;(light and) moderate&#039; and &#039;vigorous&#039; PA, classifying activities into the provided answer options of different PA intensities, recalling instances of &#039;normal&#039; activities such as walking and sitting, and calculating the total duration of more than one activity or instance of an activity. The revealed problems with the questionnaires were quite similar in different countries; profound cultural differences were not observed.&lt;/p&gt;&lt;p&gt;&lt;b&gt;CONCLUSIONS: &lt;/b&gt;Both questionnaires were difficult to answer for many respondents and rather user-unfriendly. They are designed to measure an exactness of PA quantity (frequency and duration) and intensity which would be desirable to obtain from a scientific point of view; however, respondents can hardly provide this information for cognitive reasons. Studies investigating the respondents&#039; perspective are useful for improving physical activity information based on self-reports.&lt;/p&gt;</p

Searches for violation of fundamental time reversal and space reflection symmetries in solid state experiments

The electric dipole moment (EDM) of a particle violates both time reversal (T) and space reflection (P) symmetries. There have been recent suggestions for searches of the electron EDM using solid state experiments [1,2]. These experiments could improve the sensitivity compared to present atomic and molecular experiments by several orders of magnitude. In the present paper we calculate the expected effect. We also suggest that this kind of experiment is sensitive to T,P-violation in nuclear forces and calculate effects caused by the nuclear Schiff moment. The compounds under consideration contain magnetic Gd$^{3+}$ ions and oxygen O$^{2-}$ ions. We demonstrate that the main mechanism for the T,P-odd effects is related to the penetration of the Oxygen 2p-electrons to the Gd core. All the effects are related to the deformation of the crystal lattice.Comment: 13 pages, 6 figure