9,332 research outputs found
Intermediate-mass black holes in dwarf galaxies out to redshift 2.4 in the Chandra COSMOS Legacy Survey
We present a sample of 40 AGN in dwarf galaxies at redshifts
2.4. The galaxies are drawn from the \textit{Chandra} COSMOS-Legacy survey as
having stellar masses M. Most
of the dwarf galaxies are star-forming. After removing the contribution from
star formation to the X-ray emission, the AGN luminosities of the 40 dwarf
galaxies are in the range erg
s. With 12 sources at , our sample constitutes the
highest-redshift discovery of AGN in dwarf galaxies. The record-holder is
cid\_1192, at and with erg
s. One of the dwarf galaxies has
M and is the least massive galaxy found so far to host an AGN. All
the AGN are of type 2 and consistent with hosting intermediate-mass black holes
(BHs) with masses M and typical Eddington
ratios . We also study the evolution, corrected for completeness, of AGN
fraction with stellar mass, X-ray luminosity, and redshift in dwarf galaxies
out to = 0.7. We find that the AGN fraction for M and erg s is
0.4\% for 0.3 and that it decreases with X-ray luminosity and
decreasing stellar mass. Unlike massive galaxies, the AGN fraction seems to
decrease with redshift, suggesting that AGN in dwarf galaxies evolve
differently than those in high-mass galaxies. Mindful of potential caveats, the
results seem to favor a direct collapse formation mechanism for the seed BHs in
the early Universe.Comment: 16 pages, 10 figures, accepted for publication in MNRA
Electronic structures of ZnCoO using photoemission and x-ray absorption spectroscopy
Electronic structures of ZnCoO have been investigated using
photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The
Co 3d states are found to lie near the top of the O valence band, with a
peak around eV binding energy. The Co XAS spectrum provides
evidence that the Co ions in ZnCoO are in the divalent Co
() states under the tetrahedral symmetry. Our finding indicates that the
properly substituted Co ions for Zn sites will not produce the diluted
ferromagnetic semiconductor property.Comment: 3 pages, 2 figure
Interplay between carrier and impurity concentrations in annealed GaMnAs intrinsic anomalous Hall Effect
Investigating the scaling behavior of annealed GaMnAs anomalous
Hall coefficients, we note a universal crossover regime where the scaling
behavior changes from quadratic to linear, attributed to the anomalous Hall
Effect intrinsic and extrinsic origins, respectively. Furthermore, measured
anomalous Hall conductivities when properly scaled by carrier concentration
remain constant, equal to theoretically predicated values, spanning nearly a
decade in conductivity as well as over 100 K in T. Both the qualitative
and quantitative agreement confirms the validity of new equations of motion
including the Berry phase contributions as well as tunablility of the intrinsic
anomalous Hall Effect.Comment: 4 pages, 5 figure
Putative spin liquid in the triangle-based iridate BaIrTiO
We report on thermodynamic, magnetization, and muon spin relaxation
measurements of the strong spin-orbit coupled iridate BaIrTiO,
which constitutes a new frustration motif made up a mixture of edge- and
corner-sharing triangles. In spite of strong antiferromagnetic exchange
interaction of the order of 100~K, we find no hint for long-range magnetic
order down to 23 mK. The magnetic specific heat data unveil the -linear and
-squared dependences at low temperatures below 1~K. At the respective
temperatures, the zero-field muon spin relaxation features a persistent spin
dynamics, indicative of unconventional low-energy excitations. A comparison to
the isostructural compound BaRuTiO suggests that a concerted
interplay of compass-like magnetic interactions and frustrated geometry
promotes a dynamically fluctuating state in a triangle-based iridate.Comment: Physical Review B accepte
Inhomogeneous Low Frequency Spin Dynamics in La_{1.65}Eu_{0.2}Sr_{0.15}CuO_4
We report Cu and La nuclear magnetic resonance (NMR) measurements in the
title compound that reveal an inhomogeneous glassy behavior of the spin
dynamics. A low temperature peak in the La spin lattice relaxation rate and the
``wipeout'' of Cu intensity both arise from these slow electronic spin
fluctuations that reveal a distribution of activation energies. Inhomogeneous
slowing of spin fluctuations appears to be a general feature of doped lanthanum
cuprate.Comment: 4 pages, 2 figures. Very slight modifications to figure
CLIC4, an Intracellular Chloride Channel Protein, Is a Novel Molecular Target for Cancer Therapy
Chloride intracellular channel (CLIC)4 is a p53- and tumor necrosis factor α (TNFα)-regulated chloride channel protein that is localized to the mitochondria and cytoplasm of mouse and human keratinocytes. CLIC4 protein increases in differentiating keratinocytes and in keratinocytes exposed to DNA-damaging agents and metabolic inhibitors. Increasing CLIC4 levels by transduction of recombinant CLIC4 causes apoptosis. CLIC4 translocates to the nucleus under a variety of conditions of cell stress, and nuclear CLIC4 is associated with cell cycle arrest and accelerated apoptosis. Reduction of CLIC4 and several other CLIC family members by expressing a doxycycline-regulated CLIC4 antisense also causes apoptosis in squamous cancer cell lines. Expressing antisense CLIC4 in tumors derived from transplanting these cells into nude mice inhibits tumor growth, increases tumor apoptosis, and reduces tumor cell proliferation. Co-administration of TNFα intraperitoneally enhances the tumor-inhibitory influence of CLIC4 antisense expression. Together, these results suggest that CLIC4 is important for keratinocyte viability and may be a novel target for anti-cancer therapy
Stripe structure, spectral feature and soliton gap in high Tc cuprates
We show that the lightly doped La_{2-x}Sr_{x}CuO_{4} can be described in
terms of a stripe magnetic structure or soliton picture. The internal
relationship between the recent neutron observation of the diagonal (x=0.05) to
vertical (x >= 0.06) stripe transition, which was predicted, and the
concomitant metal-insulator transition is clarified by this solitonic physics.
The phase diagram with the unidentified transition lines between
antiferromagnetic to stripe phases, the doping dependence of the modulation
period, the origin of the mid-infrared optical absorption are investigated
comparatively with other single layer systems: La_{2-x}Sr_{x}NiO_{4} and
(La,Nd)_{2-x}Sr_{x}CuO_{4}. The novel type of quasi-particles and holes is
fully responsible for metallic conduction and ultimately superconductivity.Comment: 4 pages RevTex, 5 figure
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