Resonance peak in underdoped cuprates

The magnetic susceptibility measured in neutron scattering experiments in underdoped YBa$_2$Cu$_3$O$_{7-y}$ is interpreted based on the self-consistent solution of the t-J model of a Cu-O plane. The calculations reproduce correctly the frequency and momentum dependencies of the susceptibility and its variation with doping and temperature in the normal and superconducting states. This allows us to interpret the maximum in the frequency dependence -- the resonance peak -- as a manifestation of the excitation branch of localized Cu spins and to relate the frequency of the maximum to the size of the spin gap. The low-frequency shoulder well resolved in the susceptibility of superconducting crystals is connected with a pronounced maximum in the damping of the spin excitations. This maximum is caused by intense quasiparticle peaks in the hole spectral function for momenta near the Fermi surface and by the nesting.Comment: 9 pages, 6 figure

Electronic structure and magnetism of Mn doped GaN

Mn doped semiconductors are extremely interesting systems due to their novel magnetic properties suitable for the spintronics applications. It has been shown recently by both theory and experiment that Mn doped GaN systems have a very high Curie temperature compared to that of Mn doped GaAs systems. To understand the electronic and magnetic properties, we have studied Mn doped GaN system in detail by a first principles plane wave method. We show here the effect of varying Mn concentration on the electronic and magnetic properties. For dilute Mn concentration, $d$ states of Mn form an impurity band completely separated from the valence band states of the host GaN. This is in contrast to the Mn doped GaAs system where Mn $d$ states in the gap lie very close to the valence band edge and hybridizes strongly with the delocalized valence band states. To study the effects of electron correlation, LSDA+U calculations have been performed. Calculated exchange interaction in (Mn,Ga)N is short ranged in contrary to that in (Mn,Ga)As where the strength of the ferromagnetic coupling between Mn spins is not decreased substantially for large Mn-Mn separation. Also, the exchange interactions are anisotropic in different crystallographic directions due to the presence or absence of connectivity between Mn atoms through As bonds.Comment: 6 figures, submitted to Phys. Rev.

Energy Spectrum of Bloch Electrons Under Checkerboard Field Modulations

Two-dimensional Bloch electrons in a uniform magnetic field exhibit complex energy spectrum. When static electric and magnetic modulations with a checkerboard pattern are superimposed on the uniform magnetic field, more structures and symmetries of the spectra are found, due to the additional adjustable parameters from the modulations. We give a comprehensive report on these new symmetries. We have also found an electric-modulation induced energy gap, whose magnitude is independent of the strength of either the uniform or the modulated magnetic field. This study is applicable to experimentally accessible systems and is related to the investigations on frustrated antiferromagnetism.Comment: 8 pages, 6 figures (reduced in sizes), submitted to Phys. Rev.

Identification of the lipopolysaccharide modifications controlled by the Salmonella PmrA/PmrB system mediating resistance to Fe(III) and Al(III)

Iron is an essential metal but can be toxic in excess. While several homeostatic mechanisms prevent oxygen-dependent killing promoted by Fe(II), little is known about how cells cope with Fe(III), which kills by oxygen-independent means. Several Gram-negative bacterial species harbour a regulatory system – termed PmrA/PmrB – that is activated by and required for resistance to Fe(III). We now report the identification of the PmrA-regulated determinants mediating resistance to Fe(III) and Al(III) in Salmonella enterica serovar Typhimurium. We establish that these determinants remodel two regions of the lipopolysaccharide, decreasing the negative charge of this major constituent of the outer membrane. Remodelling entails the covalent modification of the two phosphates in the lipid A region with phosphoethanolamine and 4-aminoarabinose, which has been previously implicated in resistance to polymyxin B, as well as dephosphorylation of the Hep(II) phosphate in the core region by the PmrG protein. A mutant lacking the PmrA-regulated Fe(III) resistance genes bound more Fe(III) than the wild-type strain and was defective for survival in soil, suggesting that these PmrA-regulated lipopolysaccharide modifications aid Salmonella's survival and spread in non-host environments

The structure of blocks with a Klein four defect group

We prove Erdmann’s conjecture [16] stating that every block with a Klein four defect group has a simple module with trivial source, and deduce from this that Puig’s finiteness conjecture holds for source algebras of blocks with a Klein four defect group. The proof uses the classification of finite simple groups

Competing orders in a magnetic field: spin and charge order in the cuprate superconductors

We describe two-dimensional quantum spin fluctuations in a superconducting Abrikosov flux lattice induced by a magnetic field applied to a doped Mott insulator. Complete numerical solutions of a self-consistent large N theory provide detailed information on the phase diagram and on the spatial structure of the dynamic spin spectrum. Our results apply to phases with and without long-range spin density wave order and to the magnetic quantum critical point separating these phases. We discuss the relationship of our results to a number of recent neutron scattering measurements on the cuprate superconductors in the presence of an applied field. We compute the pinning of static charge order by the vortex cores in the `spin gap' phase where the spin order remains dynamically fluctuating, and argue that these results apply to recent scanning tunnelling microscopy (STM) measurements. We show that with a single typical set of values for the coupling constants, our model describes the field dependence of the elastic neutron scattering intensities, the absence of satellite Bragg peaks associated with the vortex lattice in existing neutron scattering observations, and the spatial extent of charge order in STM observations. We mention implications of our theory for NMR experiments. We also present a theoretical discussion of more exotic states that can be built out of the spin and charge order parameters, including spin nematics and phases with `exciton fractionalization'.Comment: 36 pages, 33 figures; for a popular introduction, see http://onsager.physics.yale.edu/superflow.html; (v2) Added reference to new work of Chen and Ting; (v3) reorganized presentation for improved clarity, and added new appendix on microscopic origin; (v4) final published version with minor change

The PHENIX Experiment at RHIC

The physics emphases of the PHENIX collaboration and the design and current status of the PHENIX detector are discussed. The plan of the collaboration for making the most effective use of the available luminosity in the first years of RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program available at http://www.rhic.bnl.gov/phenix

An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics

For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types

Knockdown of zebrafish Nav1.6 sodium channel impairs embryonic locomotor activities

[[abstract]]Although multiple subtypes of sodium channels are expressed in most neurons, the specific contributions of the individual sodium channels remain to be studied. The role of zebrafish Nav1.6 sodium channels in the embryonic locomotor movements has been investigated by the antisense morpholino (MO) knockdown. MO1 and MO2 are targeted at the regions surrounding the translation start site of zebrafish Nav1.6 mRNA. MO3 is targeted at the RNA splicing donor site of exon 2. The correctly spliced Nav1.6 mRNA of MO3 morphants is 6% relative to that of the wild-type embryos. Nav1.6-targeted MO1, MO2 and MO3 attenuate the spontaneous contraction, tactile sensitivity, and swimming in comparison with a scrambled morpholino and mutated MO3 morpholino. No significant defect is observed in the development of slow muscles, the axonal projection of primary motoneurons, and neuromuscular junctions. The movement impairments caused by MO1, MO2, and MO3 suggest that the function of Nav1.6 sodium channels is essential on the normal early embryonic locomotor activities.[[notice]]補正完畢[[journaltype]]國