1,519 research outputs found
Essential Role of the Cooperative Lattice Distortion in the Charge, Orbital and Spin Ordering in doped Manganites
The role of lattice distortion in the charge, orbital and spin ordering in
half doped manganites has been investigated. For fixed magnetic ordering, we
show that the cooperative lattice distortion stabilize the experimentally
observed ordering even when the strong on-site electronic correlation is taken
into account. Furthermore, without invoking the magnetic interactions, the
cooperative lattice distortion alone may lead to the correct charge and orbital
ordering including the charge stacking effect, and the magnetic ordering can be
the consequence of such a charge and orbital ordering. We propose that the
cooperative nature of the lattice distortion is essential to understand the
complicated charge, orbital and spin ordering observed in doped manganites.Comment: 5 pages,4 figure
Quasar Clustering from SDSS DR5: Dependences on Physical Properties
Using a homogenous sample of 38,208 quasars with a sky coverage of drawn from the SDSS Data Release Five quasar catalog, we study the
dependence of quasar clustering on luminosity, virial black hole mass, quasar
color, and radio loudness. At , quasar clustering depends weakly on
luminosity and virial black hole mass, with typical uncertainty levels for the measured correlation lengths. These weak dependences are
consistent with models in which substantial scatter between quasar luminosity,
virial black hole mass and the host dark matter halo mass has diluted any
clustering difference, where halo mass is assumed to be the relevant quantity
that best correlates with clustering strength. However, the most luminous and
most massive quasars are more strongly clustered (at the level)
than the remainder of the sample, which we attribute to the rapid increase of
the bias factor at the high-mass end of host halos. We do not observe a strong
dependence of clustering strength on quasar colors within our sample. On the
other hand, radio-loud quasars are more strongly clustered than are radio-quiet
quasars matched in redshift and optical luminosity (or virial black hole mass),
consistent with local observations of radio galaxies and radio-loud type 2 AGN.
Thus radio-loud quasars reside in more massive and denser environments in the
biased halo clustering picture. Using the Sheth et al.(2001) formula for the
linear halo bias, the estimated host halo mass for radio-loud quasars is , compared to for
radio-quiet quasar hosts at .Comment: Updated version; accepted for publication in Ap
Vertical transport and electroluminescence in InAs/GaSb/InAs structures: GaSb thickness and hydrostatic pressure studies
We have measured the current-voltage (I-V) of type II InAs/GaSb/InAs double
heterojunctions (DHETs) with 'GaAs like' interface bonding and GaSb thickness
between 0-1200 \AA. A negative differential resistance (NDR) is observed for
all DHETs with GaSb thickness 60 \AA below which a dramatic change in the
shape of the I-V and a marked hysteresis is observed. The temperature
dependence of the I-V is found to be very strong below this critical GaSb
thickness. The I-V characteristics of selected DHETs are also presented under
hydrostatic pressures up to 11 kbar. Finally, a mid infra-red
electroluminescence is observed at 1 bar with a threshold at the NDR valley
bias. The band profile calculations presented in the analysis are markedly
different to those given in the literature, and arise due to the positive
charge that it is argued will build up in the GaSb layer under bias. We
conclude that the dominant conduction mechanism in DHETs is most likely to
arise out of an inelastic electron-heavy-hole interaction similar to that
observed in single heterojunctions (SHETs) with 'GaAs like' interface bonding,
and not out of resonant electron-light-hole tunnelling as proposed by Yu et al.
A Zener tunnelling mechanism is shown to contribute to the background current
beyond NDR.Comment: 8 pages 12 fig
On the Populations of Radio Galaxies with Extended Morphology at z<0.3
Extended extragalactic radio sources have traditionally been classified into
FR I and II types, based on the ratio r of the separation S between the
brightest regions on either sides of the host galaxy and the total size T of
the radio source. Here we examine the distribution of various physical
properties as a function of r of 1040 luminous radio galaxies (RGs) at z<0.3
from the SDSS, NVSS, and FIRST. About 2/3 of the RGs are lobe-dominated (LD),
and 1/3 have prominent jets. If we follow the original definition of the FR
types (a division based solely on r), FR I and FR II RGs overlap in their host
galaxy properties. However, the rare, LD sources with r>0.8 AND OIII5007 line
luminosity >10^6 Lsun are markedly different on average from the rest of the
RGs, in the sense that they are hosted in lower mass galaxies, live in
relatively sparse environments, and have higher accretion rates onto the
central SMBH. Thus these objects and the rest of RGs form a well-defined
dichotomy. Motivated by the stark differences in the nuclear emission line
properties of the RG subsamples, we suggest that the accretion rate onto the
SMBH may play the primary role in creating the different morphologies. At
relatively high accretion rates, the accretion system may produce powerful jets
that create the "classical double" morphology (roughly corresponding to the LD
sources with r>0.8 and emission lines); at lower accretion rates the jets from
a radiatively inefficient accretion flow generate radio lobes without apparent
"hot spots" at the edge (corresponding to the majority of LD sources). At
slightly lower accretion rates AND in galaxies with dense galactic structure,
sources with prominent jets result. It is possible that while the high
accretion rate systems could affect sub-Mpc scale environments, the jets from
lower accretion rate systems may efficiently suppress activity within the host
galaxies.Comment: ApJ, accepted. 20 pages, 16 figures, 4 tables. Image quality of
Figures 1 & 2 degraded due to size limits. Table 4 is available and kept
up-to-date at http://member.ipmu.jp/yen-ting.lin/RG/index.html. Higher
resolution version available at
http://member.ipmu.jp/yen-ting.lin/Data/ytlin.pd
Yeast axial-element protein, Red1, binds SUMO chains to promote meiotic interhomologue recombination and chromosome synapsis
The synaptonemal complex (SC) is a tripartite protein structure consisting of two parallel axial elements (AEs) and a central region. During meiosis, the SC connects paired homologous chromosomes, promoting interhomologue (IH) recombination. Here, we report that, like the CE component Zip1, Saccharomyces cerevisiae axial-element structural protein, Red1, can bind small ubiquitin-like modifier (SUMO) polymeric chains. The Red1–SUMO chain interaction is dispensable for the initiation of meiotic DNA recombination, but it is essential for Tel1- and Mec1-dependent Hop1 phosphorylation, which ensures IH recombination by preventing the inter-sister chromatid DNA repair pathway. Our results also indicate that Red1 and Zip1 may directly sandwich the SUMO chains to mediate SC assembly. We suggest that Red1 and SUMO chains function together to couple homologous recombination and Mec1–Tel1 kinase activation with chromosome synapsis during yeast meiosis
Gap symmetry and structure of Fe-based superconductors
The recently discovered Fe-pnictide and chalcogenide superconductors display
low-temperature properties suggesting superconducting gap structures which
appear to vary substantially from family to family, and even within families as
a function of doping or pressure. We propose that this apparent nonuniversality
can actually be understood by considering the predictions of spin fluctuation
theory and accounting for the peculiar electronic structure of these systems,
coupled with the likely 'sign-changing s-wave' (s\pm) symmetry. We review
theoretical aspects, materials properties and experimental evidence relevant to
this suggestion, and discuss which further measurements would be useful to
settle these issues.Comment: 86 pages, revie
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T cell–derived inducible nitric oxide synthase switches off TH17 cell differentiation
RORγt is necessary for the generation of TH17 cells but the molecular mechanisms for the regulation of TH17 cells are still not fully understood. We show that activation of CD4+ T cells results in the expression of inducible nitric oxide synthase (iNOS). iNOS-deficient mice displayed enhanced TH17 cell differentiation but without major effects on either TH1 or TH2 cell lineages, whereas endothelial NOS (eNOS) or neuronal NOS (nNOS) mutant mice showed comparable TH17 cell differentiation compared with wild-type control mice. The addition of N6-(1-iminoethyl)-l-lysine dihydrochloride (L-NIL), the iNOS inhibitor, significantly enhanced TH17 cell differentiation, and S-nitroso-N-acetylpenicillamine (SNAP), the NO donor, dose-dependently reduced the percentage of IL-17–producing CD4+ T cells. NO mediates nitration of tyrosine residues in RORγt, leading to the suppression of RORγt-induced IL-17 promoter activation, indicating that NO regulates IL-17 expression at the transcriptional level. Finally, studies of an experimental model of colitis showed that iNOS deficiency results in more severe inflammation with an enhanced TH17 phenotype. These results suggest that NO derived from iNOS in activated T cells plays a negative role in the regulation of TH17 cell differentiation and highlight the importance of intrinsic programs for the control of TH17 immune responses
Porphyrin Homeostasis Maintained by ABCG2 Regulates Self-Renewal of Embryonic Stem Cells
Under appropriate culture conditions, undifferentiated embryonic stem (ES) cells can undergo multiple self-renewal cycles without loss of pluripotency suggesting they must be equipped with specific defense mechanisms to ensure sufficient genetic stability during self-renewal expansion. The ATP binding cassette transporter ABCG2 is expressed in a wide variety of somatic and embryonic stem cells. However, whether it plays an important role in stem cell maintenance remains to be defined.Here we provide evidence to show that an increase in the level of ABCG2 was observed accompanied by ES colony expansion and then were followed by decreases in the level of protoporphyrin IX (PPIX) indicating that ABCG2 plays a role in maintaining porphyrin homoeostasis. RNA-interference mediated inhibition of ABCG2 as well as functional blockage of ABCG2 transporter with fumitremorgin C (FTC), a specific and potent inhibitor of ABCG2, not only elevated the cellular level of PPIX, but also arrest the cell cycle and reduced expression of the pluripotent gene Nanog. Overexpression of ABCG2 in ES cells was able to counteract the increase of endogenous PPIX induced by treatment with 5-Aminolevulinic acid suggesting ABCG2 played a direct role in removal of PPIX from ES cells. We also found that excess PPIX in ES cells led to elevated levels of reactive oxygen species which in turn triggered DNA damage signals as indicated by increased levels of gammaH2AX and phosphorylated p53. The increased level of p53 reduced Nanog expression because RNA- interference mediated inhibition of p53 was able to prevent the downregulation of Nanog induced by FTC treatment.The present work demonstrated that ABCG2 protects ES cells from PPIX accumulation during colony expansion, and that p53 and gammaH2AX acts as a downstream checkpoint of ABCG2-dependent defense machinery in order to maintain the self-renewal of ES cells
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