2014 IEEE International Conference on Bioinformatics and Biomedicine, BIBM 2014

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SU(4) Spin-Orbital Two-Leg Ladder, Square and Triangle Lattices

Based on the generalized valence bond picture, a Schwinger boson mean field theory is applied to the symmetric SU(4) spin-orbital systems. For a two-leg SU(4) ladder, the ground state is a spin-orbital liquid with a finite energy gap, in good agreement with recent numerical calculations. In two-dimensional square and triangle lattices, the SU(4) Schwinger bosons condense at (\pi/2,\pi/2) and (\pi/3,\pi/3), respectively. Spin, orbital, and coupled spin-orbital static susceptibilities become singular at the wave vectors, twice of which the bose condensation arises at. It is also demonstrated that there are spin, orbital, and coupled spin-orbital long-range orderings in the ground state.Comment: 5 page

Utilising surface-level data to explore surface, tooth, individual and family influence on the aetiology of hypomineralised second primary molars

OBJECTIVES: Hypomineralised second primary molars (HSPM) are common developmental enamel defects. The aims of this study were to use surface-level data to explore the clustering of HSPM at four levels (family, child, tooth, surface). METHODS: This study of 172 twin pairs was nested within the Peri/postnatal Epigenetic Twin Study. HSPM was measured by standardised oral examinations at age 6 years. Multilevel logistic regression models were fitted to assess the correlation structure of surface level data and variation in HSPM. The associations between surface level risk factors and HSPM were then explored using the multilevel logistic regression model using the best fitting correlation structure. RESULTS: The prevalence of HSPM was 68 (19.8%) children, with a total of 141 (10.3%) teeth and 264 tooth surfaces (6.3%) affected. Multilevel models revealed that a hierarchical structure accounting for correlation at the family, child and tooth level best accounted for the variation in HSPM. The estimated variances from the best fitting model (Model 3) were largest at the family level (12.27, 95% CI 6.68, 22.51) compared with 5.23 at the child level and 1.93 at the tooth level. Application of regression analysis utilising this three-level correlation structure identified tooth/surface level factors in addition to the previously identified familial and individual risk factors for HSPM. CONCLUSION: In addition to familial (environmental and genetic) and unique child-level factors, the aetiology of HSPM is likely to be influenced by local tooth-level factors

Encoded Universality for Generalized Anisotropic Exchange Hamiltonians

We derive an encoded universality representation for a generalized anisotropic exchange Hamiltonian that contains cross-product terms in addition to the usual two-particle exchange terms. The recently developed algebraic approach is used to show that the minimal universality-generating encodings of one logical qubit are based on three physical qubits. We show how to generate both single- and two-qubit operations on the logical qubits, using suitably timed conjugating operations derived from analysis of the commutator algebra. The timing of the operations is seen to be crucial in allowing simplification of the gate sequences for the generalized Hamiltonian to forms similar to that derived previously for the symmetric (XY) anisotropic exchange Hamiltonian. The total number of operations needed for a controlled-Z gate up to local transformations is five. A scalable architecture is proposed.Comment: 11 pages, 4 figure

Effect of cytokinins on shoot regeneration from cotyledon and leaf segment of stem mustard (Brassica juncea var. tsatsai)

Cotyledon and leaf segments of stem mustard (Brassica juncea var. tsatsai) were cultured on Murashige and Skoog medium supplemented with various concentrations of different cytokinins [6-benzyladenine (BA), N-(2-chloro-4-pyridyl)-n-phenylurea (CPPU), 6-furfurylaminopurine (KT) and thidiazuron (TDZ)] in combinations with different levels of ¿-naphthalene acetic acid (NAA). The shoot regeneration frequency of cotyledon and leaf segment was dependent on the kinds and concentrations of cytokinins used in the medium, while in most cases cotyledon gave high regeneration frequency than leaf segment. TDZ proved to be the best cytokinin to induce shoot from both cotyledon and leaf segments compared to BA, KT and CPPU. The highest frequency of shoot regeneration was 61.3¿67.9 % in cotyledon and 40.7¿52.4% in leaf segment respectively when 2.27 or 4.54 ¿M TDZ was combined with 5.37 ¿M NAA. Next to TDZ, CPPU was also very suitable to induce shoot formation both in cotyledon and leaf segment. When 1.61 ¿M CPPU was combined with 2.69 ¿M NAA, shoot regeneration frequency was 45.0% in cotyledon and 36.4% in leaf segment, respectively. It was also shown that KT and BA affected shoot regeneration from cotyledon and leaf segment, the shoot regeneration was greatly increased when NAA was added together with cytokinins. The efficient and reliable shoot regeneration system was developed in both cotyledon and leaf segments. This regeneration protocol may be applicable to the improvement of this crop by genetic engineering in the futur

Entanglement in the Quantum Heisenberg XY model

We study the entanglement in the quantum Heisenberg XY model in which the so-called W entangled states can be generated for 3 or 4 qubits. By the concept of concurrence, we study the entanglement in the time evolution of the XY model. We investigate the thermal entanglement in the two-qubit isotropic XY model with a magnetic field and in the anisotropic XY model, and find that the thermal entanglement exists for both ferromagnetic and antiferromagnetic cases. Some evidences of the quantum phase transition also appear in these simple models.Comment: 7 pages, 6 figs, revised version submitted to Phys. Rev.

Quasiparticles as composite objects in the RVB superconductor

We study the nature of the superconducting state, the origin of d-wave pairing, and elementary excitations of a resonating valence bond (RVB) superconductor. We show that the phase string formulation of the t-J model leads to confinement of bare spinon and holon excitations in the superconducting state, though the vacuum is described by the RVB state. Nodal quasiparticles are obtained as composite excitations of spinon and holon excitations. The d-wave pairing symmetry is shown to arise from short range antiferromagnetic correlations

Antiferromagnetic Heisenberg model on anisotropic triangular lattice in the presence of magnetic field

We use Schwinger boson mean field theory to study the antiferromagnetic spin-1/2 Heisenberg model on an anisotropic triangular lattice in the presence of a uniform external magnetic field. We calculate the field dependence of the spin incommensurability in the ordered spin spiral phase, and compare the results to the recent experiments in Cs$_{2}$CuCl$_{4}$ by Coldea et al. (Phys. Rev. Lett. 86, 1335 (2001)).Comment: 4 pages with 4 figures include

Spin-orbital gapped phase with least symmetry breaking in the one-dimensional symmetrically coupled spin-orbital model

To describe the spin-orbital energy gap formation in the one-dimensional symmetrically coupled spin-orbital model, we propose a simple mean field theory based on an SU(4) constraint fermion representation of spins and orbitals. A spin-orbital gapped phase is formed due to a marginally relevant spin-orbital valence bond pairing interaction. The energy gap of the spin and orbital excitations grows extremely slowly from the SU(4) symmetric point up to a maximum value and then decreases rapidly. By calculating the spin, orbital, and spin-orbital tensor static susceptibilities at zero temperature, we find a crossover from coherent to incoherent magnetic excitations as the spin-orbital coupling decreasing from large to small values.Comment: 10 pages, Revtex file, 5 figure