Contrasting the Surface Phonon Dispersion of Pb_{0.7}Sn_{0.3}Se in Its Topologically Trivial and Nontrivial Phases.

We report inelastic He atom scattering measurements of the (001) surface phonon dispersion of the topological crystalline insulator Pb_{0.7}Sn_{0.3}Se. This material exhibits a temperature-dependent topological transition, so we measure the surface dispersion curves in both the trivial and nontrivial phases. We identify that, peculiarly, most surface modes are resonances, rather than pure surface states. We find that a shear vertical surface resonance branch around 9.0 meV dramatically changes on going from the trivial to the topological phase. We associate this remarkable change with the emergence of surface Dirac fermions. We use the measured dispersion of this resonance branch to determine the corresponding mode-dependent electron-phonon coupling λ_{ν}(q).

Nematicity and Charge Order in Superoxygenated La_{2-x}Sr_{x}CuO_{4+y}.

In this Letter, we report a resonant x-ray scattering measurement of stripelike charge order in the 1/8th doped component of electronically phase-separated, orthorhombic La_{2}CuO_{4+y}. This observation is coupled to the absence of any resonant (001) peak, which at different resonant energies has been identified with the presence of low-temperature-tetragonal-like structural tilt patterns or nematicity in the CuO planes. Thus, we provide evidence that structural pinning is not necessary for the formation of static charge stripes and that the relationship between charge nematicity and stripes may not be simple.

DNA demethylation of the TIM-3 promoter is critical for its stable expression on T cells.

The T-cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) is selectively expressed on terminally differentiated T helper 1 (Th1) cells and acts as a negative regulator that terminates Th1 responses. The dysregulation of TIM-3 expression on T cells is associated with several autoimmune phenotypes and with chronic viral infections; however, the mechanism of this regulation is unclear. In this study, we investigated the effect of DNA methylation on the expression of TIM-3. By analyzing the sequences of TIM-3 promoter regions in human and mouse, we identified a CpG island within the TIM-3 promoter and demonstrated that the promoter activity was controlled by DNA methylation. Furthermore, treatment with 5-aza-2'-deoxycytidine enhanced TIM-3 expression on mouse primary CD4(+) T cells under Th0-, Th1- or Th2-polarizing conditions. Finally, pyrosequencing analysis revealed that the methylation level of the TIM-3 promoter gradually decreased after each round of T-cell polarization, and this decrease was inversely correlated with TIM-3 expression. These data suggest that the DNA methylation of the TIM-3 promoter cooperates with lineage-specific transcription factors in the control of Th-cell development. In conclusion, DNA methylation-based regulation of TIM-3 may provide novel insights into understanding the dysregulation of TIM-3 expression under pathogenic conditions.

Spin Liquid State in the 3D Frustrated Antiferromagnet PbCuTe_{2}O_{6}: NMR and Muon Spin Relaxation Studies.

PbCuTe_{2}O_{6} is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu^{2+} ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T_{1} NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.

Snapshots of Dirac fermions near the Dirac point in topological insulators.

The recent focus on topological insulators is due to the scientific interest in the new state of quantum matter as well as the technology potential for a new generation of THz optoelectronics, spintronics and quantum computations. It is important to elucidate the dynamics of the Dirac fermions in the topologically protected surface state. Hence we utilized a novel ultrafast optical pump mid-infrared probe to explore the dynamics of Dirac fermions near the Dirac point. The femtosecond snapshots of the relaxation process were revealed by the ultrafast optics. Specifically, the Dirac fermion-phonon coupling strength in the Dirac cone was found to increase from 0.08 to 0.19 while Dirac fermions were away from the Dirac point into higher energy states. Further, the energy-resolved transient reflectivity spectra disclosed the energy loss rate of Dirac fermions at room temperature was about 1 meV/ps. These results are crucial to the design of Dirac fermion devices.

B lymphocyte-induced maturation protein 1 (BLIMP-1) attenuates autoimmune diabetes in NOD mice by suppressing Th1 and Th17 cells.

AIMS/HYPOTHESIS: Recent reports indicate that B lymphocyte-induced maturation protein 1 (BLIMP-1), encoded by the Prdm1 gene, expands its control over T cells and is associated with susceptibility to colitis in mice with T cell-specific BLIMP-1 deficiency. In this study, we aimed to investigate the potential role of BLIMP-1 in regulating autoimmune diabetes and T helper type 17 (Th17) cells. METHODS: We generated T cell-specific Blimp1 (also known as Prdm1) transgenic (Tg) or conditional knockout (CKO) NOD mice, in which Blimp1 is overexpressed or deleted in T cells, respectively. By side-by-side analysing these Tg or CKO mice, we further dissected the potential mechanisms of BLIMP-1-mediated modulation on autoimmune diabetes. RESULTS: Overproduction of BLIMP-1 in T cells significantly attenuated insulitis and the incidence of diabetes in NOD mice. Consistent with these results, the diabetogenic effect of splenocytes was remarkably impaired in Blimp1 Tg mice. Moreover, overproduction of BLIMP-1 repressed the proliferation and activation of lymphocytes and enhanced the function of regulatory T cells (Tregs) in NOD mice. In contrast, mice lacking BLIMP-1 in T cells markedly increased Th1 and Th17 cells, and developed highly proliferative and activated lymphocytes. Strikingly, overexpansion of Th1 and Th17 cells in CKO mice was significantly reduced by introducing a Blimp1 transgene, reinforcing the emerging role of BLIMP-1 in autoimmunity. CONCLUSIONS/INTERPRETATION: We conclude that BLIMP-1 orchestrates a T cell-specific modulation of autoimmunity by affecting lymphocyte proliferation and activation, Th1 and Th17 cell differentiation, and Treg function. Our results provide a theoretical basis for developing BLIMP-1-manipulated therapies for autoimmune diabetes.

Evidence for dimer crystal melting in the frustrated spin-ladder system BiCu2PO6.

In the spin ladder compound BiCu(2)PO(6), there exists a decisive dynamics of spin excitations that we classify and characterize using inelastic light scattering. We observe an interladder singlet bound mode at 24 cm(-1) and two intraladder bound states at 62 and 108 cm(-1) in the leg (bb) and the rung (cc) polarization as well as a broad triplon continuum extending from 36 cm(-1) to 700 cm(-1). Though isolated spin ladder physics can roughly account for the observed excitations at high energies, frustration and interladder interactions need to be considered to fully describe the spectral distribution and scattering selection rules at low and intermediate energies. In addition, we attribute the rich spectrum of singlet bound modes to a melting of a dimer crystal. Our study provides evidence for a Z(2) quantum phase transition from a dimer to a resonating valence bond state driven by singlet fluctuations.

Measurement of unique magnetic and superconducting phases in oxygen-doped high-temperature superconductors La(2-x)Sr(x)CuO(4+y).

We present a combined magnetic neutron scattering and muon spin rotation study of the nature of the magnetic and superconducting phases in electronically phase separated La(2-x)Sr(x)CuO(4+y), x=0.04, 0.065, 0.09. For all samples, we find long-range modulated magnetic order below T(N) is approximately equal to Tc=39 K. In sharp contrast to oxygen-stoichiometric La(2-x)Sr(x)CuO(4), we find that the magnetic propagation vector as well as the ordered magnetic moment is independent of Sr content and consistent with that of the "striped" cuprates. Our study provides direct proof that superoxygenation in La(2-x)Sr(x)CuO(4+y) allows the spin stripe ordered phase to emerge and phase separate from superconducting regions with the hallmarks of optimally doped oxygen-stoichiometric La(2-x)Sr(x)CuO(4).

Electron-phonon coupling on the surface of the topological insulator Bi2Se3 determined from surface-phonon dispersion measurements.

In this Letter, we report measurements of the coupling between Dirac fermion quasiparticles (DFQs) and phonons on the (001) surface of the strong topological insulator Bi2Se3. While most contemporary investigations of this coupling have involved examining the temperature dependence of the DFQ self-energy via angle-resolved photoemission spectroscopy measurements, we employ inelastic helium-atom scattering to explore, for the first time, this coupling from the phonon perspective. Using a Hilbert transform, we are able to obtain the imaginary part of the phonon self-energy associated with a dispersive surface-phonon branch identified in our previous work [Phys. Rev. Lett. 107, 186102 (2011)] as having strong interactions with the DFQs. From this imaginary part of the self-energy we obtain a branch-specific electron-phonon coupling constant of 0.43, which is stronger than the values reported from the angle-resolved photoemission spectroscopy measurements.

Singlet-triplet excitations in the unconventional spin-Peierls TiOBr compound.

We have performed time-of-flight neutron scattering measurements on powder samples of the unconventional spin-Peierls compound TiOBr using the fine-resolution Fermi chopper spectrometer (SEQUOIA) at the Spallation Neutron Source at Oak Ridge National Laboratory. These measurements reveal two branches of magnetic excitations within the commensurate and incommensurate spin-Peierls phases, which we associate with n=1 and n=2 triplet excitations out of the singlet ground state. These results represent the first direct measurement of the singlet-triplet energy gap in TiOBr, which has a value of E(g)=21.2±1.0 meV.

Interaction of phonons and dirac fermions on the surface of Bi2Se3: a strong Kohn anomaly.

We report the first measurements of phonon dispersion curves on the (001) surface of the strong three-dimensional topological insulator Bi2Se3. The surface phonon measurements were carried out with the aid of coherent helium beam surface scattering techniques. The results reveal a prominent signature of the exotic metallic Dirac fermion quasiparticles, including a strong Kohn anomaly. The signature is manifest in a low energy isotropic convex dispersive surface phonon branch with a frequency maximum of 1.8 THz and having a V-shaped minimum at approximately 2kF that defines the Kohn anomaly. Theoretical analysis attributes this dispersive profile to the renormalization of the surface phonon excitations by the surface Dirac fermions. The contribution of the Dirac fermions to this renormalization is derived in terms of a Coulomb-type perturbation model.

Methodologies for quantifying culturable, viable, and total Legionella pneumophila in indoor air.

UNLABELLED: Legionella pneumophila, aerosolized from numerous indoor facilities (e.g., shower heads, hot tubs, spas), may cause Pontiac fever (PF) and lethal pneumonia named Legionnaires' disease (LD) in humans. Reliable methods on quantitative exposure assessment of this bioaerosol are essential for the prevention of PF and LD. Coupled with culture, ethidium monoazide with qPCR, and qPCR assays, the collection efficiency for culturable, viable, and total L. pneumophila was assessed by means of filtration sampling (IOM with gelatin filter and cassette with polycarbonate filter) and liquid-based sampling methods (BioSampler, AGI-30, MAS-100 sampler with Tween mixture and deionized water (DW)). Results show IOM/gelatin filter was comparable to cassette/polycarbonate filter (P = 0.33) and performed greater than all of tested liquid-based methods for total cell collection. On the other hand, IOM/gelatin filter obtained greater efficiencies than cassette/polycarbonate filter by a factor of 3.8-8.6 for viable cells (P = 0.0006) and two orders of magnitude for culturable cells (P = 0.00002). Further comparison between liquid impingement and filtration methods indicates the sampling by IOM/gelatin filter, AGI-30, and BioSampler with DW were the most appropriate for viable cells, while culturable cells were collected most efficiently by BioSampler/DW with periodical replenishment during the sampling. PRACTICAL IMPLICATIONS: This study recommends the most suitable methodologies for quantifying culturable, viable, and total Legionella pneumophila in indoor air. By using appropriate sampling and analytical methods, the residents and building owners are able to obtain the reliable data and further characterize the exposure risk and/or intervention efficacy against L. pneumophila. Moreover, the adoption of suitable monitoring methods also assists the investigators to explore the sources linked to PF and LD during the outbreaks. Considering reliable microbial monitoring is fundamental for epidemiological survey and risk assessment, the present information should be taken into account in assessing L. pneumophila indoors.

Transgenic expression of haem oxygenase-1 in pancreatic beta cells protects non-obese mice used as a model of diabetes from autoimmune destruction and prolongs graft survival following islet transplantation.

AIMS/HYPOTHESIS: Haem oxygenase 1 (HO-1) has strong anti-apoptotic, anti-inflammatory and antioxidative effects that help protect cells against various forms of immune attack. We investigated whether transgenic expression of Ho-1 (also known as Hmox1) in pancreatic beta cells would protect NOD mice from autoimmune damage and prolong graft survival following islet transplantation. METHODS: To evaluate the protective effect of beta cell-specific HO-1 in autoimmune diabetes, we used an insulin promoter-driven murine Ho-1 construct (pIns-mHo-1) to generate a transgenic NOD mouse. Transgene expression, insulitis and the incidence of diabetes in mice were characterised. Lymphocyte composition, the development of T helper (Th)1, Th2 and T regulatory (Treg) cells, T cell proliferation and lymphocyte-mediated disease transfer were analysed. The potential effects of transgenic islets and islet transplantation on apoptosis, inflammation and the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) were evaluated. RESULTS: Transgenic mice showed less severe insulitis and a lower incidence of diabetes than non-transgenic control littermates. Lymphocyte composition and functions were not affected. Islets from transgenic mice expressed lower levels of proinflammatory cytokines/chemokines, proapoptotic gene expression and amounts of ROS/RNS, and were more resistant to TNF-α- and IFN-γ-induced apoptosis. Islet grafts from transgenic mice also survived longer in diabetic recipients than control islets. CONCLUSIONS/INTERPRETATION: Transgenic overexpression of Ho-1 in beta cells protected NOD mice from diabetes and delayed the autoimmune destruction of islet grafts, providing valuable insight into the development of better strategies for clinical islet transplantation in patients with type 1 diabetes.

The immune response against myelin basic protein in two strains of rat with different genetic capacity to develop experimental allergic encephalomyelitis.

After challenge with guiena pig basic protein (GPBP) Lewis (Le) rats, which are homozygous for the immune response experimental allergic encephalomyelitis (Ir-EAE) gene, developed positive delayed skin tests against GPBP and the 43 residue encephalitogenic fragment (EF); in addition, Le rat lymph node cells (LNC) were stimulated and produced migration inhibitory factor (MIF) when incubated in vitro with these antigens. In contrast Brown Norway (BN) rats, which lack the Ir-EAE gene, did not develop delayed skin tests to EF and their LNC were not stimulated and did not produce MIF when incubated in vitro with EF. These observations indicate that the Ir-EAE gene controls a T-cell response against the EF. Le rats produced measurable anti-BP antibody by radioimmunoassay after primary challenge. Although no antibody was detectable in BN rats by radioimmunoassay, radioimmunoelectrophoresis indicated that a small amount of antibody was formed after primary immunization. After boosting intraperitoneally, both strains of rat exhibited a rise in anti-BP antibody; which was greater in Le rats. In both strains of rat the anti-BP antibody reacted with a portion of the molecule other than the EF. Since EF primarily evokes a T cell response, it is suggested that the EF portion of the BP molecule may contain a helper determinant in antibody production.

Molecular internalization of a region of myelin basic protein.

The conformation of myelin encephalitogenic or basic protein (BP) was investigated with a double-antibody radioimmunoassay by studying the reaction of BP or its fragments with antibodies produced in two rabbits against peptide 43-88 linked to rabbit serum albumin. Both antisera reacted well with peptide 43-88 but showed little or no reaction with BP. Absorption of these antisera with a BP-immunoadsorbent did not remove the antibody activity against peptide 43-88. Within the region of peptide 43- 88 it was shown that peptides 68-88 and 79-88 gave an equivalent or better reaction than peptide 43-88, whereas peptides 43-67 and 64-73 had very little reactivity. In the BP fragments containing region 43-88, peptide 1-88 showed the best reactivity, peptide 20-166 showed minimal reactivity, while peptide 1-115 showed none. These data document the internal position of at least a portion of peptide 43-88 and all of residues 79-88 in the BP molecule. The much greater reactivity of peptide 1-88 as compared to peptide 1-115 suggests that the region or a portion of the region of BP containing residues 89- 115 participates in the conformational alignment of BP restricting access to peptide 79-88. After absorption with BP, neither of the antisera prepared to peptide 43-88 reacted with PNS myelin in fixed tissue sections but continued to react with CNS myelin in similarly treated sections. The present findings demonstrate the need to consider the role of shielded antigenic determinants in the investigation of antigens or of immune responses.

Scanning transmission electron microscopy using selective high-order laue zones: three-dimensional atomic ordering in sodium cobaltate.

A new scanning transmission electron microscopy (STEM) imaging technique using high-order Laue zones (named HOLZ-STEM), a diffraction contrast which has been strenuously avoided or minimized in traditional STEM imaging, can be used to obtain the additional 1D periodic information along the electron propagation axis without sacrificing atomic resolution in the lateral (2D) dimension. HOLZ-STEM has been demonstrated to resolve the 3D long-range Na ordering of Na0.71CoO2. Direct evidence of spiral-like Na-trimer chains twisting along the c axis is unambiguously established in real space.

The spin-orbit-phonon coupling and crystalline elasticity of LaCoO3 perovskite.

Based on an integrated study of magnetic susceptibility, specific heat, and thermal expansion of single-crystal LaCoO3 free from cobalt and oxygen vacancies, two narrow spin gaps are identified before and after the phonon softening of gap size ΔE ∼ 0.5 meV in a CoO6-octahedral crystal electric field (CEF) and the thermally activated spin gap Q ∼ 25 meV, respectively. Significant excitation of Co3+ spins from a low-spin (LS) to a high-spin (HS) state is confirmed by the thermal activation behavior of spin susceptibility χ S of energy gap Q ∼ 25 meV, which follows a two-level Boltzmann distribution to saturate at a level of 50% LS/50% HS statistically above ∼200 K, without the inclusion of a postulated intermediate spin (IS) state. A threefold increase in the thermal expansion; coefficient (α) across the same temperature range as that of thermally activated HS population growth is identified, which implies the non-trivial spin-orbit-phonon coupling caused the bond length of Co3+(LS↔HS)-O fluctuation and the local lattice distortion. The unusually narrow gap of ΔE ∼ 0.5 meV for the CoO6 octahedral CEF between eg-t2g indicates a more isotropic negative charge distribution within the octahedral CEF environment, which is verified by the Electron Energy Loss Spectroscopy (EELS) study to show nontrivial La-O covalency.

Biologicl activity and synthesis of an encephalitogenic determinant.

A 45-residue fragment of the basic protein of myelin is encephalitogenic in the rabbit and monkey but relatively inactive in the guinea pig. Synthetic peptides containing the sequence of a tryptic peptide of the fragment Thr-Thr-His-Tyr-Gly-Ser-Leu-Pro-Gln-Lys are moderately encephalitogenic.

Spin-charge-lattice coupling in YBaCuFeO5: Optical properties and first-principles calculations.

We combined spectroscopic ellipsometry, Raman scattering spectroscopy, and first-principles calculations to explore the optical properties of YBaCuFeO5 single crystals. Measuring the optical absorption spectrum of YBaCuFeO5 at room temperature revealed a direct optical band gap at approximately 1.41 eV and five bands near 1.69, 2.47, 3.16, 4.26, and 5.54 eV. Based on first-principles calculations, the observed optical excitations were appropriately assigned. Analysis of the temperature dependence of the band gap indicated anomalies in antiferromagnetic phase transition at 455 and 175 K. Additionally, a hardening in the frequency of the Eg phonon mode was observed at 175 K. The value of the spin-phonon coupling constant was 15.7 mRy/Å2. These results suggest a complex nature of spin-charge-lattice interactions in YBaCuFeO5.

Crystal growth and transport properties of Weyl semimetal TaAs.

We report the single crystal growth and transport properties of a Weyl semimetal TaAs. Unsaturated large magnetoresistance of about 22 100% at 2 K and 9 T is observed. From the Hall measurement, carrier concentrations n = 4.608 × 1024 m-3 and p = 3.099 × 1024 m-3, and mobilities µ p = 2.502 m2 V-1 s-1 and µ n = 16.785 m2 V-1 s-1 at 2 K are extracted. The de Haas-van Alphen oscillations at 2 K and 9 T suggest the presence of a Fermi surface, and the quantum electronic parameters such as effective cyclotron mass and Dingle temperature were obtained using Lifshitz-Kosevich fitting. Temperature dependent resistivity measurements at different static magnetic fields suggest the formation of an insulating gap in the Weyl semimetal TaAs. An angle-resolved photoemission spectroscopy study reveals Fermi arc surface states with different shaped features such as a long elliptical contour around each [Formula: see text] point, a bowtie-shaped contour around each [Formula: see text] point, and a crescent-shaped feature near the midpoint of each [Formula: see text] line.