Enhanced Bound State Formation in Two Dimensions via Stripe-Like Hopping Anisotropies

We have investigated two-electron bound state formation in a square two-dimensional t-J-U model with hopping anisotropies for zero electron density; these anisotropies are introduced to mimic the hopping energies similar to those expected in stripe-like arrangements of holes and spins found in various transition metal oxides. In this report we provide analytical solutions to this problem, and thus demonstrate that bound-state formation occurs at a critical exchange coupling, J_c, that decreases to zero in the limit of extreme hopping anisotropy t_y/t_x -> 0. This result should be contrasted with J_c/t = 2 for either a one-dimensional chain, or a two-dimensional plane with isotropic hopping. Most importantly, this behaviour is found to be qualitatively similar to that of two electrons on the two-leg ladder problem in the limit of t_interchain/t_intrachain -> 0. Using the latter result as guidance, we have evaluated the pair correlation function, thus determining that the bound state corresponds to one electron moving along one chain, with the second electron moving along the opposite chain, similar to two electrons confined to move along parallel, neighbouring, metallic stripes. We emphasize that the above results are not restricted to the zero density limit - we have completed an exact diagonalization study of two holes in a 12 X 2 two-leg ladder described by the t-J model and have found that the above-mentioned lowering of the binding energy with hopping anisotropy persists near half filling.Comment: 6 pages, 3 eps figure

Genome-wide analyses of Liberibacter species provides insights into evolution, phylogenetic relationships, and virulence factors.

'Candidatus Liberibacter' species are insect-transmitted, phloem-limited α-Proteobacteria in the order of Rhizobiales. The citrus industry is facing significant challenges due to huanglongbing, associated with infection from 'Candidatus Liberibacter asiaticus' (Las). In order to gain greater insight into 'Ca. Liberibacter' biology and genetic diversity, we have performed genome sequencing and comparative analyses of diverse 'Ca. Liberibacter' species, including those that can infect citrus. Our phylogenetic analysis differentiates 'Ca. Liberibacter' species and Rhizobiales in separate clades and suggests stepwise evolution from a common ancestor splitting first into nonpathogenic Liberibacter crescens followed by diversification of pathogenic 'Ca. Liberibacter' species. Further analysis of Las genomes from different geographical locations revealed diversity among isolates from the United States. Our phylogenetic study also indicates multiple Las introduction events in California and spread of the pathogen from Florida to Texas. Texan Las isolates were closely related, while Florida and Asian isolates exhibited the most genetic variation. We have identified conserved Sec translocon (SEC)-dependent effectors likely involved in bacterial survival and virulence of Las and analysed their expression in their plant host (citrus) and insect vector (Diaphorina citri). Individual SEC-dependent effectors exhibited differential expression patterns between host and vector, indicating that Las uses its effector repertoire to differentially modulate diverse organisms. Collectively, this work provides insights into the evolution of 'Ca. Liberibacter' species, the introduction of Las in the United States and identifies promising Las targets for disease management

Deflection of coronal rays by remote CMEs: shock wave or magnetic pressure?

We analyze five events of the interaction of coronal mass ejections (CMEs) with the remote coronal rays located up to 90^\circ away from the CME as observed by the SOHO/LASCO C2 coronagraph. Using sequences of SOHO/LASCO C2 images, we estimate the kink propagation in the coronal rays during their interaction with the corresponding CMEs ranging from 180 to 920 km/s within the interval of radial distances form 3 R. to 6 R. . We conclude that all studied events do not correspond to the expected pattern of shock wave propagation in the corona. Coronal ray deflection can be interpreted as the influence of the magnetic field of a moving flux rope related to a CME. The motion of a large-scale flux rope away from the Sun creates changes in the structure of surrounding field lines, which are similar to the kink propagation along coronal rays. The retardation of the potential should be taken into account since the flux rope moves at high speed comparable with the Alfven speed.Comment: Accepted for Publication in Solar Physic

Comparison of Genomes of Three Xanthomonas oryzae Bacteriophages

<p>Abstract</p> <p>Background</p> <p>Xp10 and OP1 are phages of <it>Xanthomonas oryzae </it>pv. oryzae (Xoo), the causative agent of bacterial leaf blight in rice plants, which were isolated in 1967 in Taiwan and in 1954 in Japan, respectively. We recently isolated the Xoo phage Xop411.</p> <p>Results</p> <p>The linear Xop411 genome (44,520 bp, 58 ORFs) sequenced here is 147 bp longer than that of Xp10 (60 ORFs) and 735 bp longer than that of OP1 (59 ORFs). The G+C contents of OP1 (51%) and Xop411 and Xp10 (52% each) are less than that of the host (65%). The 9-bp 3'-overhangs (5'-GGACAGTCT-3') in Xop411 and Xp10 are absent from OP1. More of the deduced Xop411 proteins share higher degrees of identity with Xp10 than with OP1 proteins, while the right end of the genomes of Xp10 and OP1, containing all predicted promoters, share stronger homology. Xop411, Xp10, and OP1 contain 8, 7, and 6 freestanding HNH endonuclease genes, respectively. These genes can be classified into five groups depending on their possession of the HNH domain (HNN or HNH type) and/or AP2 domain in intact or truncated forms. While the HNN-AP2 type endonuclease genes dispersed in the genome, the HNH type endonuclease genes, each with a unique copy, were located within the same genome context. Mass spectrometry and N-terminal sequencing showed nine Xop411 coat proteins, among which three were identified, six were assigned as coat proteins (4) and conserved phage proteins (2) in Xp10. The major coat protein, in which only the N-terminal methionine is removed, appears to exist in oligomeric forms containing 2 to 6 subunits. The three phages exhibit different patterns of domain duplication in the N-terminus of the tail fiber, which are involved in determination of the host range. Many short repeated sequences are present in and around the duplicated domains.</p> <p>Conclusion</p> <p>Geographical separation may have confined lateral gene transfer among the Xoo phages. The HNN-AP2 type endonucleases were more likely to transfer their genes randomly in the genome and may degenerate after successful transmission. Some repeated sequences may be involved in duplication/loss of the domains in the tail fiber genes.</p

Topological Superfluid in one-dimensional Ultracold Atomic System with Spin-Orbit Coupling

We propose a one-dimensional Hamiltonian $H_{1D}$ which supports Majorana fermions when $d_{x^{2}-y^{2}}$-wave superfluid appears in the ultracold atomic system and obtain the phase-separation diagrams both for the time-reversal-invariant case and time-reversal-symmetry-breaking case. From the phase-separation diagrams, we find that the single Majorana fermions exist in the topological superfluid region, and we can reach this region by tuning the chemical potential $\mu$ and spin-orbit coupling $\alpha_{R}$. Importantly, the spin-orbit coupling has realized in ultracold atoms by the recent experimental achievement of synthetic gauge field, therefore, our one-dimensional ultra-cold atomic system described by $H_{1D}$ is a promising platform to find the mysterious Majorana fermions.Comment: 5 papers, 2 figure

Isotopic Grand Unification with the Inclusion of Gravity (revised version)

We introduce a dual lifting of unified gauge theories, the first characterized by the isotopies, which are axiom- preserving maps into broader structures with positive-definite generalized units used for the representation of matter under the isotopies of the Poincare' symmetry, and the second characterized by the isodualities, which are anti-isomorphic maps with negative-definite generalized units used for the representation of antimatter under the isodualities of the Poincare' symmetry. We then submit, apparently for the first time, a novel grand unification with the inclusion of gravity for matter embedded in the generalized positive-definite units of unified gauge theories while gravity for antimatter is embedded in the isodual isounit. We then show that the proposed grand unification provides realistic possibilities for a resolution of the axiomatic incompatibilities between gravitation and electroweak interactions due to curvature, antimatter and the fundamental space-time symmetries.Comment: 20 pages, Latex, revised in various details and with added reference

Ground State Properties of the Doped 3-Leg t-J Ladder

Results for a doped 3-leg t-J ladder obtained using the density matrix renormalization group are reported. At low hole doping, the holes form a dilute gas with a uniform density. The momentum occupation of the odd band shows a sharp decrease at a large value of k_F similar to the behavior of a lightly doped t-J chain, while the even modes appear gapped. The spin-spin correlations decay as a power law consistent with the absence of a spin gap, but the pair field correlations are negligible. At larger doping we find evidence for a spin gap and as x increases further we find 3-hole diagonal domain walls. In this regime there are pair field correlations and the internal pair orbital has d_x^2-y^2 - like symmetry. However, the pair field correlations appear to fall exponentially at large distances.Comment: 14 pages, 11 postscript figure