Spin-orbital gap of multiorbital antiferromagnet

In order to discuss the spin-gap formation in a multiorbital system, we analyze an e_g-orbital Hubbard model on a geometrically frustrated zigzag chain by using a density-matrix renormalization group method. Due to the appearance of a ferro-orbital arrangement, the system is regarded as a one-orbital system, while the degree of spin frustration is controlled by the spatial anisotropy of the orbital. In the region of strong spin frustration, we observe a finite energy gap between ground and first-excited states, which should be called a spin-orbital gap. The physical meaning is clarified by an effective Heisenberg spin model including correctly the effect of the orbital arrangement influenced by the spin excitation.Comment: 8 pages, 6 figures, extended versio

Structure and apparent topography of TiO2 (110) surfaces

We present self-consistent ab-initio total-energy and electronic-structure calculations on stoichiometric and non-stoichiometric TiO2 (110) surfaces. Scanning tunneling microscopy (STM) topographs are simulated by calculating the local electronic density of states over an energy window appropriate for the experimental positive-bias conditions. We find that under these conditions the STM tends to image the undercoordinated Ti atoms, in spite of the physical protrusion of the O atoms, giving an apparent reversal of topographic contrast on the stoichiometric 1x1 or missing-row 2x1 surface. We also show that both the interpretation of STM images and the direct comparison of surface energies favor an added-row structure over the missing-row structure for the oxygen-deficient 2x1 surface.Comment: 6 pages, two-column style with 5 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/index.html#ng_tio

Spin, charge, and orbital correlations in the one-dimensional t2g-orbital Hubbard model

We present the zero-temperature phase diagram of the one-dimensional t2g-orbital Hubbard model, obtained using the density-matrix renormalization group and Lanczos techniques. Emphasis is given to the case for the electron density n=5 corresponding to five electrons per site, of relevance for some Co-based compounds. However, several other cases for electron densities between n=3 and 6 are also studied. At n=5, our results indicate a first-order transition between a paramagnetic (PM) insulator phase and a fully-polarized ferromagnetic (FM) state by tuning the Hund's coupling. The results also suggest a transition from the n=5 PM insulator phase to a metallic regime by changing the electron density, either via hole or electron doping. The behavior of the spin, charge, and orbital correlation functions in the FM and PM states are also described in the text and discussed. The robustness of these two states varying parameters suggests that they may be of relevance in more realistic higher dimensional systems as well.Comment: 9 pages, 8 figure

Multipole correlations of t2gt_{\rm 2g}-orbital Hubbard model with spin-orbit coupling

We investigate the ground-state properties of a one-dimensional $t_{\rm 2g}$-orbital Hubbard model including an atomic spin-orbit coupling by using numerical methods, such as Lanczos diagonalization and density-matrix renormalization group. As the spin-orbit coupling increases, we find a ground-state transition from a paramegnetic state to a ferromagnetic state. In the ferromagnetic state, since the spin-orbit coupling mixes spin and orbital states with complex number coefficients, an antiferro-orbital state with complex orbitals appears. According to the appearance of the complex orbital state, we observe an enhancement of $\Gamma_{4u}$ octupole correlations.Comment: 3 pages, 3 figures, To appear in J. Phys. Soc. Jpn. Suppl., Proceedings of ICHE2010 (September 17-20, 2010, Hachioji, Japan

Superconductivity emerging near quantum critical point of valence transition

The nature of the quantum valence transition is studied in the one-dimensional periodic Anderson model with Coulomb repulsion between f and conduction electrons by the density-matrix renormalization group method. It is found that the first-order valence transition emerges with the quantum critical point and the crossover from the Kondo to the mixed-valence states is strongly stabilized by quantum fluctuation and electron correlation. It is found that the superconducting correlation is developed in the Kondo regime near the sharp valence increase. The origin of the superconductivity is ascribed to the development of the coherent motion of electrons with enhanced valence fluctuation, which results in the enhancement of the charge velocity, but not of the charge compressibility. Statements on the valence transition in connection with Ce metal and Ce compounds are given.Comment: 9 pages, 4 figure

The effect of different fertilizer application levels on anthocyanoplast development in berry skin of Pione grapevines (V. vinifera x V. labrusca)

Effects of different levels of a complete liquid fertilizer on grape berry coloration and anthocyanoplast (ACP) development in the skin were investigated. Four-year-old vines of cv. Pione (a tetraploid hybrid of Vitis vinifera L. and V. labrusca L.) were planted in root zone-restricted beds and were treated with normal (N), high (H; Nx1.5), and excessively high (EH; Nx2) levels of a commercial liquid fertilizer. Fertilizer levels were decreased to one third after veraison to accelerate berry ripening. Skin anthocyanin contents in N- and H-treated berries increased at a constant rate after veraison, while the contents in EH berries were significantly lower. ACPs were first observed in epidermal cells at veraison in N and H berries and 2 weeks later in EH berries. In each treatment formation of ACPs in hypodermal cells occurred one week later than in epidermal cells. In each treatment the number of epidermal cells containing ACPs increased during ripening of the berries but the number of hypodermal cells with ACPs increased only in N vines. The average numbers of ACPs per epidermal and hypodermal cell were largest in N vines, followed by H and EH vines (two weeks after veraison). The number of ACPs decreased thereafter because most ACPs coalesced. The average ACP diameter at full ripeness was 16.7 μm in N vines, whereas in H and EH vines it was 9.5 μm and 9.7 μm, respectively. From these results, it can be deduced that in Pione grape berries high fertilizer levels inhibit ACP formation both in epidermal and hypodermal cells at veraison and/or induce their coalescence thereafter, resulting in poor coloration.

Economic evaluation of the effect of selected crop practices on nonagricultural uses of water

Cropping systems may have an unfavorable influence on the quality of nearby surface water. In this study, linear programming methods were used to assess the impact of improvements in certain water quality characteristics on economically optimal crop systems. Thus, the effect of crop practices on water quality is analyzed indirectly by assuming that farmers would alter their cropping practices in the most economical way in order to conform to various water-quality constraints. A 1,200-acre watershed was used to illustrate the procedure. Sediment entering the reservoir was treated as a variable constraint on maximization of farm income. Requiring successively lower amounts of sediment to enter the reservoir caused farm income to decrease at an increasing rate. The analysis was enlarged to include a constraint on nitrate in the leachate below the root zone. This phase of the analysis also included a charge for removing at least some of the sediment entering the reservoir. As the nitrate limit on the leachate was lowered, farm income decreased at an increasing rate. The requirement of removal of the sediment by itself had little or no effect on the nitrate concentration in the leachate. Extensions of the procedure for use in other situations are suggested.U.S. Geological SurveyU.S. Department of the InteriorOpe

Resting energy expenditure and physical activity level of rice farmers in Lao PDR during the post-harvest season

Objective: To estimate the daily physical activity level (PAL) of traditional rice farmers in rural Lao PDR during a post-harvest season.Design: Cross-sectional study.Setting: A rice-farming village in Savannakhet Province, Lao PDR.Subjects: 12 husband/wife pairs.Interventions: Resting energy expenditure (REE) while sitting was measured by indirect calorimetry, and anthropometric indices were recorded. The total daily energy expenditure (TEE) and daily step frequency (STP) were estimated by accelerometry. PAL values were derived from TEE and REE values.Results: The mean REE (kcal/day) was significantly (P < 0.0001) higher for men (1,899 ± 227) than for women (1496 ± 139). The difference between men and women was reduced when adjusted for body weight by an analysis of covariance and became non-significant after adjustment for fat-free mass. The mean PAL values of the subjects were relatively low (1.77 and 1.71 for men and women, respectively) compared with those of ricefarming populations observed during intensive agricultural seasons. A significant negative relationship was found between the physical activity indices (TEE and STP) and the percentage of body fat, but not between these indices and the body mass index (BMI).Conclusions: PAL values of Lao rice farmers were relatively low during the post-harvest season. A better understanding of their behavioral and energetic adaptations will require estimates of both time allocation and energy expenditure. Maximization of food security will require surveys of physical activity, diet, and nutritional status during intensive agricultural seasons, which are associated with high PAL values and a negative energy balance