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Expression of natural killer receptor alleles at different Ly49 loci occurs independently and is regulated by major histocompatibility complex class I molecules.
Ly49 receptor genes are expressed by subsets of natural killer (NK) cells in an overlapping fashion, accounting for the capacity of NK subsets to attack host cells that have selectively downregulated self-major histocompatibility complex (MHC) class I molecules. It was shown previously that most NK cells express only one or the other allele of a given Ly49 gene, while a smaller population expresses both alleles. However, the methods used to detect monoallelic and biallelic cells were nonquantitative. Here, new allele-specific antibodies were used to provide the first quantitative examination of biallelic and monoallelic expression of Ly49A and Ly49G2. The results demonstrate conclusively that most Ly49A(+) and Ly49G2(+) NK cells express the corresponding gene in a monoallelic fashion, with a smaller subset expressing both alleles. Unexpectedly, biallelic Ly49A(+) NK cells were more numerous than predicted by completely independent allelic expression, suggesting some heterogeneity among NK progenitors in the potential to express a given Ly49 gene. The data also show that cells expressing one allele of Ly49G2 may express Ly49A from the same or opposite chromosome with equal likelihood, indicating that the expressed allele is chosen independently for different Ly49 genes. Finally, the data demonstrate that biallelic expression of Ly49A or Ly49G2 occurs least frequently in mice that express ligands for these receptors (H-2(d) mice), and most frequently in class I-deficient mice. Thus, biallelic expression of Ly49 genes is regulated by interactions of NK cell progenitors with MHC class I molecules
Electronic charges and electric potential at LaAlO3/SrTiO3 interfaces studied by core-level photoemission spectroscopy
We studied LaAlO3/SrTiO3 interfaces for varying LaAlO3 thickness by
core-level photoemission spectroscopy. In Ti 2p spectra for conducting "n-type"
interfaces, Ti3+ signals appeared, which were absent for insulating "p-type"
interfaces. The Ti3+ signals increased with LaAlO3 thickness, but started well
below the critical thickness of 4 unit cells for metallic transport. Core-level
shifts with LaAlO3 thickness were much smaller than predicted by the polar
catastrophe model. We attribute these observations to surface
defects/adsorbates providing charges to the interface even below the critical
thickness
Chemical potential jump between hole- and electron-doped sides of ambipolar high-Tc cuprate
In order to study an intrinsic chemical potential jump between the hole- and
electron-doped high-Tc superconductors, we have performed core-level X-ray
photoemission spectroscopy (XPS) measurements of Y0.38La0.62Ba1.74La0.26Cu3Oy
(YLBLCO), into which one can dope both holes and electrons with maintaining the
same crystal structure. Unlike the case between the hole-doped system
La_2-xSrxCuO4 and the electron-doped system Nd_2-xCexCuO4, we have estimated
the true chemical potential jump between the hole- and electron-doped YLBLCO to
be ~0.8 eV, which is much smaller than the optical gaps of 1.4-1.7 eV reported
for the parent insulating compounds. We attribute the reduced jump to the
indirect nature of the charge-excitation gap as well as to the polaronic nature
of the doped carriers.Comment: 4 pages, 3 figure
Chemical potential shift induced by double-exchange and polaronic effects in Nd_{1-x}Sr_xMnO_3
We have studied the chemical potential shift as a function of temperature in
NdSrMnO (NSMO) by measurements of core-level photoemission
spectra. For ferromagnetic samples ( and 0.45), we observed an unusually
large upward chemical potential shift with decreasing temperature in the
low-temperature region of the ferromagnetic metallic (FM) phase. This can be
explained by the double-exchange (DE) mechanism if the band is split by
dynamical/local Jahn-Teller effect. The shift was suppressed near the Curie
temperature (), which we attribute to the crossover from the DE to
lattice-polaron regimes.Comment: 5 pages, 6 figure
Non-Thermal Emission from Relativistic Electrons in Clusters of Galaxies: A Merger Shock Acceleration Model
We have investigated evolution of non-thermal emission from relativistic
electrons accelerated at around the shock fronts during merger of clusters of
galaxies. We estimate synchrotron radio emission and inverse Compton scattering
of cosmic microwave background photons from extreme ultraviolet (EUV) to hard
X-ray range. The hard X-ray emission is most luminous in the later stage of
merger. Both hard X-ray and radio emissions are luminous only while signatures
of merging events are clearly seen in thermal intracluster medium (ICM). On the
other hand, EUV radiation is still luminous after the system has relaxed.
Propagation of shock waves and bulk-flow motion of ICM play crucial roles to
extend radio halos. In the contracting phase, radio halos are located at the
hot region of ICM, or between two substructures. In the expanding phase, on the
other hand, radio halos are located between two ICM hot regions and shows
rather diffuse distribution.Comment: 19 pages, 5 figures, accepted for publication in Ap
Photoemission study of TiO2/VO2 interfaces
We have measured photoemission spectra of two kinds of TiO-capped VO
thin films, namely, that with rutile-type TiO (r-TiO/VO) and that
with amorphous TiO (a-TiO/VO) capping layers. Below the
Metal-insulator transition temperature of the VO thin films, K,
metallic states were not observed for the interfaces with TiO, in contrast
with the interfaces between the band insulator SrTiO and the Mott insulator
LaTiO in spite of the fact that both TiO and SrTiO are band
insulators with electronic configurations and both VO and LaTiO
are Mott insulators with electronic configurations. We discuss possible
origins of this difference and suggest the importance of the polarity
discontinuity of the interfaces. Stronger incoherent part was observed in
r-TiO/VO than in a-TiO/VO, suggesting Ti-V atomic diffusion due
to the higher deposition temperature for r-TiO/VO.Comment: 5 pages, 6 figure
Spectroscopy and Imaging Performance of the Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT)
LXeGRIT is a balloon-borne Compton telescope based on a liquid xenon time
projection chamber (LXeTPC) for imaging cosmic \g-rays in the energy band of
0.2-20 MeV. The detector, with 400 cm area and 7 cm drift gap, is filled
with high purity LXe. Both ionization and scintillation light signals are
detected to measure the energy deposits and the three spatial coordinates of
individual \g -ray interactions within the sensitive volume. The TPC has been
characterized with repeated measurements of its spectral and Compton imaging
response to \g -rays from radioactive sources such as \na, \cs, \yt and Am-Be.
The detector shows a linear response to \g -rays in the energy range 511 keV
-4.4 MeV, with an energy resolution (FWHM) of \Delta E/E=8.8% \: \sqrt{1\MeV
/E}. Compton imaging of \yt \g -ray events with two detected interactions is
consistent with an angular resolution of 3 degrees (RMS) at 1.8 MeV.Comment: To appear in: Hard X-Ray, Gamma-Ray and Neutron Detector Physics XI,
2000; Proc. SPIE, vol. 4140; K.A. Flanagan & O.H. Siegmund, ed
Sigma Exchange in the Nonmesonic Decays of Light Hypernuclei and Violation of the Delta I=1/2 Rule
Nonmesonic weak decays of s-shell hypernuclei are analyzed in microscopic
models for the Lambda N to NN weak interaction. A scalar-isoscalar meson,
sigma, is introduced and its importance in accounting the decay rates, n/p
ratios and proton asymmetry is demonstrated. Possible violation of the Delta
I=1/2 rule in the nonmesonic weak decay of Lambda is discussed in a
phenomenological analysis and several useful constraints are presented. The
microscopic calculation shows that the current experimental data indicate a
large violation of the Delta I=1/2 rule, although no definite conclusion can be
derived due to large ambiguity of the decay rate of {^4_Lambda H}.Comment: 13 pages, 5 figure
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