930 research outputs found
The sixth Painleve equation arising from D_4^{(1)} hierarchy
The sixth Painleve equation arises from a Drinfel'd-Sokolov hierarchy
associated with the affine Lie algebra of type D_4 by similarity reduction.Comment: 14 page
Competition between Magnetic and Structural Transition in CrN
CrN is observed to undergo a paramagnetic to antiferromagnetic transition
accompanied by a shear distortion from cubic NaCl-type to orthorhombic
structure. Our first-principle plane wave and ultrasoft pseudopotential
calculations confirm that the distorted antiferromagnetic phase with spin
configuration arranged in double ferromagnetic sheets along [110] is the most
stable. Antiferromagnetic ordering leads to a large depletion of states around
Fermi level, but it does not open a gap. Simultaneous occurence of structural
distortion and antiferromagnetic order is analyzed.Comment: 10 pages, 10 figure
Exploration of a 100 TeV gamma-ray northern sky using the Tibet air-shower array combined with an underground water-Cherenkov muon-detector array
Aiming to observe cosmic gamma rays in the 10 - 1000 TeV energy region, we
propose a 10000 m^2 underground water-Cherenkov muon-detector (MD) array that
operates in conjunction with the Tibet air-shower (AS) array. Significant
improvement is expected in the sensitivity of the Tibet AS array towards
celestial gamma-ray signals above 10 TeV by utilizing the fact that
gamma-ray-induced air showers contain far fewer muons compared with
cosmic-ray-induced ones. We carried out detailed Monte Carlo simulations to
assess the attainable sensitivity of the Tibet AS+MD array towards celestial
TeV gamma-ray signals. Based on the simulation results, the Tibet AS+MD array
will be able to reject 99.99% of background events at 100 TeV, with 83% of
gamma-ray events remaining. The sensitivity of the Tibet AS+MD array will be
~20 times better than that of the present Tibet AS array around 20 - 100 TeV.
The Tibet AS+MD array will measure the directions of the celestial TeV
gamma-ray sources and the cutoffs of their energy spectra. Furthermore, the
Tibet AS+MD array, along with imaging atmospheric Cherenkov telescopes as well
as the Fermi Gamma-ray Space Telescope and X-ray satellites such as Suzaku and
MAXI, will make multiwavelength observations and conduct morphological studies
on sources in the quest for evidence of the hadronic nature of the cosmic-ray
acceleration mechanism.Comment: Accepted by Astroparticle Physic
Induction of microRNAs, mir-155, mir-222, mir-424 and mir-503, promotes monocytic differentiation through combinatorial regulation
Acute myeloid leukemia (AML) involves a block in terminal differentiation of
the myeloid lineage and uncontrolled proliferation of a progenitor state. Using
phorbol myristate acetate (PMA), it is possible to overcome this block in THP-1
cells (an M5-AML containing the MLL-MLLT3 fusion), resulting in differentiation
to an adherent monocytic phenotype. As part of FANTOM4, we used microarrays to
identify 23 microRNAs that are regulated by PMA. We identify four PMA-induced
micro- RNAs (mir-155, mir-222, mir-424 and mir-503) that when overexpressed
cause cell-cycle arrest and partial differentiation and when used in
combination induce additional changes not seen by any individual microRNA. We
further characterize these prodifferentiative microRNAs and show that mir-155
and mir-222 induce G2 arrest and apoptosis, respectively. We find mir-424 and
mir-503 are derived from a polycistronic precursor mir-424-503 that is under
repression by the MLL-MLLT3 leukemogenic fusion. Both of these microRNAs
directly target cell-cycle regulators and induce G1 cell-cycle arrest when
overexpressed in THP-1. We also find that the pro-differentiative mir-424 and
mir-503 downregulate the anti-differentiative mir-9 by targeting a site in its
primary transcript. Our study highlights the combinatorial effects of multiple
microRNAs within cellular systems.Comment: 45 pages 5 figure
Excitons and charged excitons in semiconductor quantum wells
A variational calculation of the ground-state energy of neutral excitons and
of positively and negatively charged excitons (trions) confined in a
single-quantum well is presented. We study the dependence of the correlation
energy and of the binding energy on the well width and on the hole mass. The
conditional probability distribution for positively and negatively charged
excitons is obtained, providing information on the correlation and the charge
distribution in the system. A comparison is made with available experimental
data on trion binding energies in GaAs-, ZnSe-, and CdTe-based quantum well
structures, which indicates that trions become localized with decreasing
quantum well width.Comment: 9 pages, 11 figure
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