Coexistence and Interaction of Spinons and Magnons in an Antiferromagnet with Alternating Antiferromagnetic and Ferromagnetic Quantum Spin Chains.

In conventional quasi-one-dimensional antiferromagnets with quantum spins, magnetic excitations are carried by either magnons or spinons in different energy regimes: they do not coexist independently, nor could they interact with each other. In this Letter, by combining inelastic neutron scattering, quantum Monte Carlo simulations, and random phase approximation calculations, we report the discovery and discuss the physics of the coexistence of magnons and spinons and their interactions in Botallackite-Cu_{2}(OH)_{3}Br. This is a unique quantum antiferromagnet consisting of alternating ferromagnetic and antiferromagnetic spin-1/2 chains with weak interchain couplings. Our study presents a new paradigm where one can study the interaction between two different types of magnetic quasiparticles: magnons and spinons.

Endometriosis and the microbiome: a systematic review.

BACKGROUND: The aetiology and pathogenesis of endometriosis are still under investigation. There is evidence that there is a complex bidirectional interaction between endometriosis and the microbiome. OBJECTIVE: To systematically review the available literature on the endometriosis-microbiome interaction, with the aim of guiding future inquiries in this emerging area of endometriosis research. SEARCH STRATEGY: MEDLINE, Embase, Scopus and Web of Science were searched through May 2019. A manual search of reference lists of relevant studies was also performed. SELECTION CRITERIA: Published and unpublished literature in any language describing a comparison of the microbiome state in mammalian hosts with and without endometriosis. DATA COLLECTION AND ANALYSIS: Identified studies were screened and assessed independently by two authors. Data were extracted and compiled in a qualitative synthesis of the evidence. MAIN RESULTS: Endometriosis appears to be associated with an increased presence of Proteobacteria, Enterobacteriaceae, Streptococcus spp. and Escherichia coli across various microbiome sites. The phylum Firmicutes and the genus Gardnerella also appear to have an association; however, this remains unclear. CONCLUSIONS: The complex bidirectional relationship between the microbiome and endometriosis has begun to be characterised by the studies highlighted in this systematic review. Laboratory and clinical studies demonstrate that there are indeed differences in the microbiome composition of hosts with and without endometriosis. TWEETABLE ABSTRACT: Review findings show endometriosis associated with increased Proteobacteria, Enterobacteriaceae, Streptococcus and Escherichia coli across various microbiome sites.

Quantum spin liquid emerging in two-dimensional correlated Dirac fermions.

At sufficiently low temperatures, condensed-matter systems tend to develop order. A notable exception to this behaviour is the case of quantum spin liquids, in which quantum fluctuations prevent a transition to an ordered state down to the lowest temperatures. There have now been tentative observations of such states in some two-dimensional organic compounds, yet quantum spin liquids remain elusive in microscopic two-dimensional models that are relevant to experiments. Here we show, by means of large-scale quantum Monte Carlo simulations of correlated fermions on a honeycomb lattice (a structure realized in, for example, graphene), that a quantum spin liquid emerges between the state described by massless Dirac fermions and an antiferromagnetically ordered Mott insulator. This unexpected quantum-disordered state is found to be a short-range resonating valence-bond liquid, akin to the one proposed for high-temperature superconductors: the possibility of unconventional superconductivity through doping therefore arises in our system. We foresee the experimental realization of this model system using ultra-cold atoms, or group IV elements arranged in honeycomb lattices.

Interaction-Driven Metal-Insulator Transition in Strained Graphene.

The question of whether electron-electron interactions can drive a metal to insulator transition in graphene under realistic experimental conditions is addressed. Using three representative methods to calculate the effective long-range Coulomb interaction between π electrons in graphene and solving for the ground state using quantum Monte Carlo methods, we argue that, without strain, graphene remains metallic and changing the substrate from SiO_{2} to suspended samples hardly makes any difference. In contrast, applying a rather large-but experimentally realistic-uniform and isotropic strain of about 15% seems to be a promising route to making graphene an antiferromagnetic Mott insulator.

Understanding the Josephson current through a Kondo-correlated quantum dot.

We study the Josephson current 0-π transition of a quantum dot tuned to the Kondo regime. The physics can be quantitatively captured by the numerically exact continuous time quantum Monte Carlo method applied to the single-impurity Anderson model with Bardeen-Cooper-Schrieffer superconducting leads. For a comparison to an experiment, the tunnel couplings are determined by fitting the normal-state linear conductance. Excellent agreement for the dependence of the critical Josephson current on the level energy is achieved. For increased tunnel couplings the Kondo scale becomes comparable to the superconducting gap, and the regime of the strongest competition between superconductivity and Kondo correlations is reached; we predict the gate voltage dependence of the critical current in this regime.

Correlation effects in quantum spin-Hall insulators: a quantum Monte Carlo study.

We consider the Kane-Mele model supplemented by a Hubbard U term. The phase diagram is mapped out using projective auxiliary field quantum Monte Carlo simulations. The quantum spin liquid of the Hubbard model is robust against weak spin-orbit interaction, and is not adiabatically connected to the spin-Hall insulating state. Beyond a critical value of U>U(c) both states are unstable toward magnetic ordering. In the quantum spin-Hall state we study the spin, charge, and single-particle dynamics of the helical Luttinger liquid by retaining the Hubbard interaction only on a ribbon edge. The Hubbard interaction greatly suppresses charge currents along the edge and promotes edge magnetism but leaves the single-particle signatures of the helical liquid intact.

Coherent heavy quasiparticles in a CePt5 surface alloy.

We report on the results of a high-resolution angle-resolved photoemission study on the ordered surface alloy CePt(5). The temperature dependence of the spectra show the formation of the coherent low-energy heavy-fermion band near the Fermi level. These experimental data are supported by a multiband model calculation in the framework of the dynamical mean-field theory.

High prevalence of HBV genotype D in Syria and the clinical characteristics of hepatitis B e antigen-negative chronic hepatitis B.

Hepatitis B virus (HBV) genotype D and hepatitis B e antigen (HBeAg) negative chronic hepatitis are the most prevalent in Mediterranean countries. No data have ever been published on their prevalence in Syria, a country of intermediate endemicity for HBV. The aims of the current study were to determine the HBV genotype distribution in Syria, the prevalence of HBeAg-positive and HBeAg-negative chronic hepatitis and to analyse the clinical characteristics of each group. A total of 220 patients were included. Ninety-seven percent of the patients were of genotype D, and 72% were HBeAg negative. The HBeAg-negative patients were older, had a lower viral load, had more cirrhosis and the mode of contamination was known less than for HBeAg-positive patients. These findings have major implications in understanding the natural history of the infection and are of great relevance in the choice of therapy.

The cytokinesis gene KEULE encodes a Sec1 protein that binds the syntaxin KNOLLE.

KEULE is required for cytokinesis in Arabidopsis thaliana. We have positionally cloned the KEULE gene and shown that it encodes a Sec1 protein. KEULE is expressed throughout the plant, yet appears enriched in dividing tissues. Cytokinesis-defective mutant sectors were observed in all somatic tissues upon transformation of wild-type plants with a KEULE-green fluorescent protein gene fusion, suggesting that KEULE is required not only during embryogenesis, but at all stages of the plant's life cycle. KEULE is characteristic of a Sec1 protein in that it appears to exist in two forms: soluble or peripherally associated with membranes. More importantly, KEULE binds the cytokinesis-specific syntaxin KNOLLE. Sec1 proteins are key regulators of vesicle trafficking, capable of integrating a large number of intra- and/or intercellular signals. As a cytokinesis-related Sec1 protein, KEULE appears to represent a novel link between cell cycle progression and the membrane fusion apparatus.

Response to Comment on "The role of electron-electron interactions in two-dimensional Dirac fermions".

Hesselmann et al question one of our conclusions: the suppression of Fermi velocity at the Gross-Neveu critical point for the specific case of vanishing long-range interactions and at zero energy. The possibility they raise could occur in any finite-size extrapolation of numerical data. Although we cannot definitively rule out this possibility, we provide mathematical bounds on its likelihood.

The role of electron-electron interactions in two-dimensional Dirac fermions.

The role of electron-electron interactions in two-dimensional Dirac fermion systems remains enigmatic. Using a combination of nonperturbative numerical and analytical techniques that incorporate both the contact and long-range parts of the Coulomb interaction, we identify the two previously discussed regimes: a Gross-Neveu transition to a strongly correlated Mott insulator and a semimetallic state with a logarithmically diverging Fermi velocity accurately described by the random phase approximation. We predict that experimental realizations of Dirac fermions span this crossover and that this determines whether the Fermi velocity is increased or decreased by interactions. We explain several long-standing mysteries, including why the observed Fermi velocity in graphene is consistently about 20% larger than values obtained from ab initio calculations and why graphene on different substrates shows different behaviors.

The Arabidopsis KNOLLE and KEULE genes interact to promote vesicle fusion during cytokinesis.

Partitioning of the cytoplasm during cytokinesis or cellularisation requires syntaxin-mediated membrane fusion [1-3]. Whereas in animals, membrane fusion promotes ingression of a cleavage furrow from the plasma membrane [4,5], somatic cells of higher plants form de novo a transient membrane compartment, the cell plate, which is initiated in the centre of the division plane and matures into a new cell wall and its flanking plasma membranes [6,7]. Cell plate formation results from the fusion of Golgi-derived vesicles delivered by a dynamic cytoskeletal array, the phragmoplast. Mutations in two Arabidopsis genes, KNOLLE (KN) and KEULE (KEU), cause abnormal seedlings with multinucleate cells and incomplete cell walls [1,8]. The KN gene encodes a cytokinesis-specific syntaxin which localises to the cell plate [9]. Here, we show that KN protein localisation is unaffected in keu mutant cells, which, like kn, display phragmoplast microtubules and accumulate ADL1 protein in the plane of cell division but vesicles fail to fuse with one another. Genetic interactions between KN and KEU were analysed in double mutant embryos. Whereas the haploid gametophytes gave rise to functional gametes, the embryos behaved like single cells displaying multiple, synchronously cycling nuclei, cell cycle-dependent microtubule arrays and ADL1 accumulation between pairs of daughter nuclei. This complete inhibition of cytokinesis from fertilisation indicates that KN and KEU, have partially redundant functions and interact specifically in vesicle fusion during cytokinesis of somatic cells.

Matching DMFT calculations with photoemission spectra of heavy fermion insulators: universal properties of the near-gap spectra of SmB6.

Paramagnetic heavy fermion insulators consist of fully occupied quasiparticle bands inherent to Fermi liquid theory. The gap emergence below a characteristic temperature is the ultimate sign of coherence for a many-body system, which in addition can induce a non-trivial band topology. Here, we demonstrate a simple and efficient method to compare a model study and an experimental result for heavy fermion insulators. The temperature dependence of the gap formation in both local moment and mixed valence regimes is captured within the dynamical mean field (DMFT) approximation to the periodic Anderson model (PAM). Using the topological coherence temperature as the scaling factor and choosing the input parameter set within the mixed valence regime, we can unambiguously link the theoretical energy scales to the experimental ones. As a particularly important result, we find improved consistency between the scaled DMFT density of states and the photoemission near-gap spectra of samarium hexaboride (SmB6).

Of weeds and men: what genomes teach us about plant cell biology.

It has generally been assumed that fundamental cellular processes are conserved at the molecular level. Genome comparisons, however, suggest that the molecular mechanisms underlying programmed cell death, defense, adaptation and development may differ considerably between the plant and animal kingdoms. Phylogenetic analyses have revealed a great deal of novelty in the plant genes that are implicated in conserved processes such as transcription, cytoskeletal dynamics and vesicle trafficking. The Arabidopsis genome highlights the highly dynamic and regulated nature of the plant cell, which is fine-tuned to light, water, nutrient availability, temperature, touch and wind.

Somatic and germinal recombination of a direct repeat in Arabidopsis.

Homologous recombination between a pair of directly repeated transgenes was studied in Arabidopsis. The test construct included two different internal, non-overlapping deletion alleles of npt (neomycin phosphotransferase) flanking an active HPT (hygromycin phosphotransferase) gene. This construct was introduced into Arabidopsis by agrobacterium-mediated transformation with selection for resistance to hygromycin, and two independent single-insert lines were analyzed. Selection for active NPT by resistance to kanamycin gave both fully and partly (chimeric) recombinant seedlings. Rates for one transgenic line were estimated at less than 2 x 10(-5) events per division for germinal and greater than 10(-6) events per division for somatic recombination, a much smaller difference than between meiotic and mitotic recombination in yeast. Southern analysis showed that recombinants could be formed by either crossing over or gene conversion. A surprisingly high fraction (at least 2/17) of the recombinants, however, appeared to result from the concerted action of two or more independent simple events. Some evolutionary implications are discussed.

Effects of Pluronic F-68 on Tetrahymena cells: protection against chemical and physical stress and prolongation of survival under toxic conditions.

The effects of the non-ionic surfactant Pluronic F-68 (0.01% w/v) on Tetrahymena cells have been studied. A marked protection against chemical and physical stress was observed. The chemical stress effects were studied in cells suspended in buffer (starvation) or in buffers with added ingredients from a chemically defined medium (Ca2+, Mg2+, Na+, K+, trace metal ions). The physical stress was due to mechanical stress or hyperthermia. The data show that Pluronic: (a) prolongs the survival of low concentration cell suspensions during starvation; (b) prevents the cell death caused by low concentrations of Ca2+ (70 microM); (c) prolongs the survival of cells exposed to higher ion concentrations (10 mM Ca2+, or Na+ or K+); (d) postpones the death caused by trace metal ions like Zn2+, Fe3+ and, Cu2+; (e) protects cells from the death caused by shearing forces; and (f) prolongs the survival of cells exposed to hyperthermia (43 degrees C). The cellular survival is increased at reduced temperatures (e.g. 4 degrees C instead of 36 degrees C) and at increased cellular concentrations (e.g. 100 cells ml(-1) instead of 25 or 10 cells ml(-1)). There is no effect of pre-incubation with Pluronic. The protective effect of Pluronic towards Tetrahymena is observed for concentrations in the range from 0.001 to 0.1% w/v.

[International influenza surveillance (author's transl)]. / Surveillance internationale de la grippe.

Influenza may be considered a convenient model to set up a methodology for surveillance in a country, which can further be extended to other diseases. The solidarity which exists among Directors of National Influenza Centres is one of the reasons for its success. On positive result, and one which is not negligible, has been the stimulating effect which influenza surveillance had on the development of virus laboratories in tropical regions.

[International surveillance of some viral diseases (author's transl)]. / Surveillance internationale de certaines maladies à virus.

During a period of more than fifteen years the WHO international surveillance system for selected viral diseases has been modified on several occasions. The aims of the surveillance programme on viral diseases are two-fold: to make available world-wide epidemiological information and to contribute to the development of public health laboratories in countries where this is necessary.

Correlation effects in two-dimensional topological insulators.

Topological insulators have become one of the most active research areas in condensed matter physics. This article reviews progress on the topic of electronic correlation effects in the two-dimensional case, with a focus on systems with intrinsic spin-orbit coupling and numerical results. Topics addressed include an introduction to the noninteracting case, an overview of theoretical models, correlated topological band insulators, interaction-driven phase transitions, topological Mott insulators and fractional topological states, correlation effects on helical edge states, and topological invariants of interacting systems.