109 research outputs found
Nitric oxide, cell multiplication, and cell survival
Arrest of cell division is crucial for cells to enter a program of terminal differentiation. In the developing organ or a differentiating tissue, growth arrest defines roughly the size of the cellular population that is further committed to become a domain of differentiated cells. Eventually, the balance between the number of cell divisions and the extent of subsequent programmed cell death determines the final size of a domain, a tissue, or an organ (for review, see Bryant and Simpson 1984; Raff 1992, 1996). Mitogenesis, cytostasis, and survival of neuronal cells can be induced and maintained by the same or by different growth or trophic factors. The signaling pathways that coordinate proliferation, growth arrest, and survival of cells and groups of cells in developing organisms are not known, but they probably involve as yet undetermined inter- and intra-cellular second messenger molecules
Phase Change Observed in Ultrathin Ba0.5Sr0.5TiO3 Films by in-situ Resonant Photoemission Spectroscopy
Epitaxial Ba0.5Sr0.5TiO3 thin films were prepared on Nb-doped SrTiO3
(100)substrates by the pulsed laser deposition technique, and were studied by
measuring the Ti 2p - 3d resonant photoemission spectra in the valence-band
region as a function of film thickness, both at room temperature and low
temperature. Our results demonstrated an abrupt variation in the spectral
structures between 2.8 nm (~7 monolayers) and 2.0 nm (~5 monolayers)
Ba0.5Sr0.5TiO3 films, suggesting that there exists a critical thickness for
phase change in the range of 2.0 nm to 2.8 nm. This may be ascribed mainly to
the intrinsic size effects.Comment: 13 pages, 4 figure
Photoemission and x-ray absorption studies of valence states in (Ni,Zn,Fe,Ti)O thin films exhibiting photo-induced magnetization
By means of photoemission and x-ray absorption spectroscopy, we have studied
the electronic structure of (Ni,Zn,Fe,Ti)O thin films, which
exhibits a cluster glass behavior with a spin-freezing temperature of
K and photo-induced magnetization (PIM) below . The Ni and Zn
ions were found to be in the divalent states. Most of the Fe and Ti ions in the
thin films were trivalent (Fe) and tetravalent (Ti),
respectively. While Ti doping did not affect the valence states of the Ni and
Zn ions, a small amount of Fe ions increased with Ti concentration,
consistent with the proposed charge-transfer mechanism of PIM.Comment: 4 pages, 4 figure
Soft x-ray magnetic circular dichroism study of weakly ferromagnetic ZnVO thin film
We performed a soft x-ray magnetic circular dichroism (XMCD) study of a
ZnVO thin film which showed small ferromagnetic moment. Field and
temperature dependences of V 2 XMCD signals indicated the coexistence of
Curie-Weiss paramagnetic, antiferromagnetic, and possibly ferromagnetic V ions,
quantitatively consistent with the magnetization measurements. We attribute the
paramagnetic signal to V ions substituting Zn sites which are somewhat
elongated along the c-axis
Electronic structure and magnetism of the diluted magnetic semiconductor Fe-doped ZnO nano-particles
We have studied the electronic structure of ZnFeO
nano-particles, which have been reported to show ferromagnetism at room
temperature, by x-ray photoemission spectroscopy (XPS), resonant photoemission
spectroscopy (RPES), x-ray absorption spectroscopy (XAS) and x-ray magnetic
circular dichroism (XMCD). From the experimental and cluster-model calculation
results, we find that Fe atoms are predominantly in the Fe ionic state
with mixture of a small amount of Fe and that Fe ions are
dominant in the surface region of the nano-particles. It is shown that the room
temperature ferromagnetism in the ZnFeO nano-particles is
primarily originated from the antiferromagnetic coupling between unequal
amounts of Fe ions occupying two sets of nonequivalent positions in the
region of the XMCD probing depth of 2-3 nm.Comment: Single column, 12 pages, 8 figures, 1 tabl
Angle-resolved photoemission study of MX-chain compound [Ni(chxn)Br]Br
We report on the results of angle-resolved photoemission experiments on a
quasi-one-dimensional -chain compound [Ni(chxn)Br]Br (chxn =
1,2-cyclohexanediamine), a one-dimensional Heisenberg system with
and K, which shows a gigantic non-linear optical effect. A "band"
having about 500 meV energy dispersion is found in the first half of the
Brillouin zone , but disappears at . Two
dispersive features, expected from the spin-charge separation, as have been
observed in other quasi-one-dimensional systems like SrCuO, are not
detected. These characteristic features are well reproduced by the -
chain model calculations with a small charge-transfer energy compared
with that of one-dimensional Cu-O based compounds. We propose that this smaller
is the origin of the absence of clear spin- and charge-separation in
the photoemission spectra and strong non-linear optical effect in
[Ni(chxn)Br]Br.Comment: 4 pages, 3 figure
Local electronic structure of Cr in the II-VI diluted ferromagnetic semiconductor ZnCrTe
The electronic structure of the Cr ions in the diluted ferromagnetic
semiconductor ZnCrTe ( and 0.15) thin films has been
investigated using x-ray magnetic circular dichroism (XMCD) and photoemission
spectroscopy (PES). Magnetic-field () and temperature () dependences of
the Cr XMCD spectra well correspond to the magnetization measured by a
SQUID magnetometer. The line shape of the Cr XMCD spectra is independent
of , , and , indicating that the ferromagnetism is originated from the
same electronic states of the Cr ion. Cluster-model analysis indicates that
although there are two or more kinds of Cr ions in the ZnCrTe
samples, the ferromagnetic XMCD signal is originated from Cr ions substituted
for the Zn site. The Cr 3d partial density of states extracted using Cr resonant PES shows a broad feature near the top of the valence band,
suggesting strong ,- hybridization. No density of states is detected
at the Fermi level, consistent with their insulating behavior. Based on these
findings, we conclude that double exchange mechanism cannot explain the
ferromagnetism in ZnCrTe.Comment: Accepted for New Journal of Physics. Single column, 21 pages, 7
figure
Electronic structure of GaCrN and Si-doping effects studied by photoemission and X-ray absorption spectroscopy
The electronic structure of the magnetic semiconductor GaCrN
and the effect of Si doping on it have been investigated by photoemission and
soft x-ray absorption spectroscopy. We have confirmed that Cr in GaN is
predominantly trivalent substituting for Ga, and that Cr 3 states appear
within the band gap of GaN just above the N 2-derived valence-band maximum.
As a result of Si doping, downward shifts of the core levels (except for Cr
2) and the formation of new states near the Fermi level were observed, which
we attribute to the upward chemical potential shift and the formation of a
small amount of Cr species caused by the electron doping. Possibility of
Cr-rich cluster growth by Si doping are discussed based on the spectroscopic
and magnetization data.Comment: 5 pages, 3 figure
High molecular diversity of the fungus Guignardia citricarpa and Guignardia mangiferae and new primers for the diagnosis of the citrus black spot
Efficacy of exome-targeted capture sequencing to detect mutations in known cerebellar ataxia genes
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