523 research outputs found
On Sasaki-Einstein manifolds in dimension five
We prove the existence of Sasaki-Einstein metrics on certain simply connected
5-manifolds where until now existence was unknown. All of these manifolds have
non-trivial torsion classes. On several of these we show that there are a
countable infinity of deformation classes of Sasaki-Einstein structures.Comment: 18 pages, Exposition was expanded and a reference adde
Mutant CEBPA: Priming Stem Cells for Myeloid Leukemogenesis
In a recent study published in Cancer Cell, Bereshchenko and colleagues (2009) report a knockin mouse model that represents the most frequently occurring biallelic combination of CEBPA mutations found in human acute myeloid leukemia
PU.1 and Junb: Suppressing the formation of acute myeloid leukemia stem cells
Improved understanding of the molecular pathways that suppress the genesis and maintenance of cancer stem cells will facilitate development of rationally targeted therapies. PU.1 is a transcription factor that is required for normal myelomonocytic differentiation in hematopoiesis, and reduced PU.1 activity has been associated with myeloid leukemogenesis in man and in mouse models. A recent study by Steidl et al. demonstrates that Junb and Jun, two AP-1 transcription factors, are critical downstream effectors of the tumor suppressor activity of PU.1, and that reduced expression of Junb, in particular, may be a common feature of acute myeloid leukemogenesis
Hard-Thermal-Loop Corrections in Leptogenesis I: CP-Asymmetries
We investigate hard-thermal-loop (HTL) corrections to the CP-asymmetries in
neutrino and, at high temperature, Higgs boson decays in leptogenesis. We pay
special attention to the two leptonic quasiparticles that arise at non-zero
temperature and find that there are four contributions to the CP-asymmetries,
which correspond to the four combinations of the two leptonic quasiparticles in
the loop and in the final states. In two additional cases, we approximate the
full HTL-lepton propagator with a zero-temperature propagator that employs the
thermal lepton mass m_l(T), or the asymptotic thermal lepton mass sqrt{2}
m_l(T). We find that the CP-asymmetries in the one-mode approaches differ by up
to one order of magnitude from the full two-mode treatment in the interesting
temperature regime T \sim M_1. The asymmetry in Higgs boson decays turns out to
be two orders of magnitude larger than the asymmetry in neutrino decays in the
zero-temperature treatment. The effect of HTL corrections on the final lepton
asymmetry are investigated in paper II of this series.Comment: 38 pages, 14 figure
Geometric Suppression of Single-Particle Energy Spacings in Quantum Antidots
Quantum Antidot (AD) structures have remarkable properties in the integer
quantum Hall regime, exhibiting Coulomb-blockade charging and the Kondo effect
despite their open geometry. In some regimes a simple single-particle (SP)
model suffices to describe experimental observations while in others
interaction effects are clearly important, although exactly how and why
interactions emerge is unclear. We present a combination of experimental data
and the results of new calculations concerning SP orbital states which show how
the observed suppression of the energy spacing between states can be explained
through a full consideration of the AD potential, without requiring any effects
due to electron interactions such as the formation of compressible regions
composed of multiple states, which may occur at higher magnetic fields. A full
understanding of the regimes in which these effects occur is important for the
design of devices to coherently manipulate electrons in edge states using AD
resonances.Comment: 4 pages, 2 figure
Shapley Supercluster Survey: Ram-pressure stripping versus tidal interactions in the Shapley supercluster
We present two new examples of galaxies undergoing transformation in the Shapley supercluster core. These low-mass (M⋆∼0.4--1×1010M⋆∼0.4--1×1010 M⊙) galaxies are members of the two clusters SC 1329−313 (z ∼ 0.045) and SC 1327−312 (z ∼ 0.049). Integral-field spectroscopy complemented by imaging in the ugriK bands and in Hα narrow band is used to disentangle the effects of tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies, SOS 61086 and SOS 90630, we observe one-sided extraplanar ionized gas extending respectively ∼30 and ∼41 kpc in projection from their discs. The galaxies' gaseous discs are truncated, and the kinematics of the stellar and gas components are decoupled, supporting the RPS scenario. The emission of the ionized gas extends in the direction of a possible companion for both galaxies suggesting a TI. The overall gas velocity field of SOS 61086 is reproduced by ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and starting ∼250 Myr ago, consistent with the age of the young stellar populations. A link between the observed gas stripping and the cluster–cluster interaction experienced by SC 1329−313 and A3562 is suggested. Simulations of ram pressure acting almost edge-on are able to fully reproduce the gas velocity field of SOS 90630, but cannot at the same time reproduce the extended tail of outflowing gas. This suggests that an additional disturbance from a TI is required. This study adds a piece of evidence that RPS may take place in different environments with different impacts and witnesses the possible effect of cluster–cluster merger on RPS
Surface-Initiated Atom Transfer Radical Polymerization Induced Transformation of Selenium Nanowires into Copper Selenide@Polystyrene Core-Shell Nanowires
This Article reports the first preparation of cuprous and cupric selenide nanowires coated with a ∼5 nm thick sheath of polystyrene (copper selenide@polystyrene). These hybrid nanostructures are prepared by the transformation of selenium nanowires in a one-pot reaction, which is performed under ambient conditions. The composition, purity, and crystallinity of the copper selenide@polystyrene products were assessed by scanning transmission electron microscopy, electron energy-loss spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy techniques. We determined that the single crystalline selenium nanowires are converted into polycrystalline copper selenide@polystyrene nanowires containing both cuprous selenide and cupric selenide. The product is purified through the selective removal of residual, non-transformed selenium nanowires by performing thermal evaporation below the decomposition temperature of these copper selenides. Powder X-ray diffraction of the purified copper selenide nanowires@polystyrene identified the presence of hexagonal, cubic, and orthorhombic phases of copper selenide. These purified cuprous and cupric selenide@polystyrene nanowires have an indirect bandgap of 1.44 eV, as determined by UV–vis absorption spectroscopy. This new synthesis of polymer-encapsulated nanoscale materials may provide a method for preparing other complex hybrid nanostructures
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