Predominant Magnetic States in Hubbard Model on Anisotropic Triangular Lattices

Using an optimization variational Monte Carlo method, we study the half-filled-band Hubbard model on anisotropic triangular lattices, as a continuation of the preceding study [J. Phys. Soc. Jpn 75, 074707 (2006)]. We introduce two new trial states: (i) A coexisting state of (\pi,\pi)-antiferromagnetic (AF) and a d-wave singlet gaps, in which we allow for a band renormalization effect, and (ii) a state with an AF order of 120^\circ spin structure. In both states, a first-order metal-to-insulator transition occurs at smaller U/t than that of the pure d-wave state. In insulating regimes, magnetic orders always exist; an ordinary (\pi,\pi)-AF order survives up to t'/t\sim 0.9 (U/t=12), and a 120^\circ-AF order becomes dominant for t'/t \gsim 0.9. The regimes of the robust superconductor and of the nonmagnetic insulator the preceding study proposed give way to these magnetic domains.Comment: 11 pages, 14 figure

Is the nature of magnetic order in copper-oxides and in iron-pnictides different?

We use the results of first-principles electronic structure calculations and a strong coupling perturbation approach, together with general theoretical arguments, to illustrate the differences in super-exchange interactions between the copper-oxides and iron-pnictides. We show that the two magnetic ground states can be understood in a simple manner within the same theoretical foundation. Contrary to the emerging view that magnetic order in the iron-pnictides is of itinerant nature, we argue that the observed magnetic moment is small because of frustration introduced by the electrons of the Fe orbitals as they compete to impose their preferred magnetic ordering.Comment: 5 pages, 5 figure

Chemical trends of superconducting properties in pyrochlore oxides

Chemical trends of fundamental superconducting parameters and normal-state properties are described for a family of pyrochlore oxide superconductors. Particularly, the change of Tc from 1.0 K for alpha-pyrochlore Cd2Re2O7 to 3.3 K (A = Cs), 6.3 K (Rb), and 9.6 K (K) for beta-pyrochlore AOs2O6 is discussed on the basis of the conventional BCS scheme. Enhanced Tc and anomalous features observed for KOs2O6 are ascribed to low-energy phonons probably coming from the rattling of the K cations.Comment: 8 pages, to be published in the Proceedings of M2S-HTSC2006 (Physica C

Variational Monte Carlo studies of a t-J model on an anisotropic triangular lattice

With the insulating phase of \kappa-(BEDT-TTF)_2X in mind, we study a t-J model on an anisotropic triangular lattice, where the hopping integral is t' in one of the three directions, using a variational Monte Carlo method. By changing the value of t'/t, we study the stability of superconducting (SC) states with d- and d+id-wave symmetries and of an antiferromagnetic (AF) state. As t'/t decreases from 1, the stable state immediately switches from the d+id wave to the d wave. The AF state is stabilized from the normal spin liquid state for t'/t\lsim 0.7 at half filling. We also take account of Nagaoka ferromagnetism and a phase separation.Comment: 4 pages, 3 figure

Characterizations of ordered semigroups in terms of (∈, ∈ ∨q)-fuzzy interior ideals

In this paper, we give characterizations of ordered semigroups in terms of (∈, ∈ ∨q)-fuzzy interior ideals. We characterize different classes regular (resp. intra-regular, simple and semisimple) ordered semigroups in terms of (∈, ∈ ∨q)-fuzzy interior ideals (resp. (∈, ∈ ∨q)-fuzzy ideals). In this regard, we prove that in regular (resp. intra-regular and semisimple) ordered semigroups the concept of (∈, ∈ ∨q)-fuzzy ideals and (∈, ∈ ∨q)-fuzzy interior ideals coincide. We prove that an ordered semigroup S is simple if and only if it is (∈, ∈ ∨q)-fuzzy simple. We characterize intra-regular (resp. semisimple) ordered semigroups in terms of (∈, ∈ ∨q)-fuzzy ideals (resp. (∈, ∈ ∨q)-fuzzy interior ideals). Finally, we consider the concept of implication-based fuzzy interior ideals in an ordered semigroup, in particular, the implication operators in Lukasiewicz system of continuous-valued logic are discussed

Age and growth of Anguilla interioris leptocephali collected in Indonesian waters

Anguilla interiorisis has been only known to be distributed in northern New Guinea, but recent sampling surveys for leptocephali and the development of species identification techniques using DNA analysis have discovered that this species also appears to occur off Sumatra in the eastern Indian Ocean, and may be present in other areas of the Indonesian Archipelago. To reveal the ages and early life histories of this species, the otolith microstructure of the leptocephali collected near the Sulawesi Island and off Sumatra of Indonesia were examined. The otolith microstructure of the A. interioris leptocephali was similar to other anguillid species and showed narrow increment widths (0.49-0.58μm) near the core that increased (1.14-1.34μm) before decreasing again until the otolith edge (0.51-0.83μm), except in the smallest specimen (12.4mm TL) collected off Sumatra, which had no peak. The range of Sr: Ca ratios in their otoliths were 8.37 to 14.01. Their ages were 19d for the smallest specimen from off Sumatra, 85d for the specimen (48.9mm TL) from Tomini Bay, and 85 to 94d for the three specimens (43.4-46.5mm TL) from the Molucca Sea. The overall growth rate of the leptocephali was 0.48mm/d, and this value was intermediate compared with the growth rates of the other anguillid species. The age of the smallest A. interioris leptocephalus collected off Sumatra and the geographic patterns of currents in the regions, suggest that it was spawned in the Indian Ocean and that it may belong to a different population than the New Guinea population

FGF2 Has Distinct Molecular Functions from GDNF in the Mouse Germline Niche

Both glial cell line-derived neurotrophic factor (GDNF) and fibroblast growth factor 2 (FGF2) are bona fide self-renewal factors for spermatogonial stem cells, whereas retinoic acid (RA) induces spermatogonial differentiation. In this study, we investigated the functional differences between FGF2 and GDNF in the germline niche by providing these factors using a drug delivery system in vivo. Although both factors expanded the GFRA1+ subset of undifferentiated spermatogonia, the FGF2-expanded subset expressed RARG, which is indispensable for proper differentiation, 1.9-fold more frequently than the GDNF-expanded subset, demonstrating that FGF2 expands a differentiation-prone subset in the testis. Moreover, FGF2 acted on the germline niche to suppress RA metabolism and GDNF production, suggesting that FGF2 modifies germline niche functions to be more appropriate for spermatogonial differentiation. These results suggest that FGF2 contributes to induction of differentiation rather than maintenance of undifferentiated spermatogonia, indicating reconsideration of the role of FGF2 in the germline niche

Correspondence between otolith microstructual changes and early life history events in Anguilla marmorata leptocephali and glass eels

To determine the exact correspondence between otolith characteristics and early life history events such as metamorphosis, coastal migration and recruitment to estuaries, both otolith microstructure and microchemistry analyses were applied to a sequential developmental series of samples, e. g. leptocephali, a metamorphosing larva, oceanic glass eels, and coastal glass eels. Total length and age were 10.1-50.7 mm and 22-137 d in leptocephali, 46.3 mm and 147 d in a metamorphosing larva, 47.8, 48.6 mm and 159, 160 d in oceanic glass eels, and 47.9-54.8 mm and 119-168 d in coastal glass eels. Checks at hatching and first feeding were observed in all specimens, but metamorphosis and freshwater checks were observed only in some specimens. It was confirmed that the abrupt drop in otolith Sr : Ca ratios and drastic increases of otolith increment widths in the metamorphosing larval stage correspond to the onset of metamorphosis, and the decrease after the peaks suggested the completion of metamorphosis, because the metamorphosing larva had no decrease in incremental widths. The relatively conserved Sr : Ca ratios decreased sharply in synchrony with the increasing increment widths. This study provides the first direct evidence that these drastic changes in otolith microstructure and microchemistry actually occur during metamorphosis, which has been only hypothesized

Seasonal pigment fluctuation in diploid and polyploid Arabidopsis revealed by machine learning-based phenotyping method PlantServation

Long-term field monitoring of leaf pigment content is informative for understanding plant responses to environments distinct from regulated chambers but is impractical by conventional destructive measurements. We developed PlantServation, a method incorporating robust image-acquisition hardware and deep learning-based software that extracts leaf color by detecting plant individuals automatically. As a case study, we applied PlantServation to examine environmental and genotypic effects on the pigment anthocyanin content estimated from leaf color. We processed >4 million images of small individuals of four Arabidopsis species in the field, where the plant shape, color, and background vary over months. Past radiation, coldness, and precipitation significantly affected the anthocyanin content. The synthetic allopolyploid A. kamchatica recapitulated the fluctuations of natural polyploids by integrating diploid responses. The data support a long-standing hypothesis stating that allopolyploids can inherit and combine the traits of progenitors. PlantServation facilitates the study of plant responses to complex environments termed "in natura"