635 research outputs found
The CP-PACS Project and Lattice QCD Results
The aim of the CP-PACS project was to develop a massively parallel computer
for performing numerical research in computational physics with primary
emphasis on lattice QCD. The CP-PACS computer with a peak speed of 614 GFLOPS
with 2048 processors was completed in September 1996, and has been in full
operation since October 1996. We present an overview of the CP-PACS project and
describe characteristics of the CP-PACS computer. The CP-PACS has been mainly
used for hadron spectroscopy studies in lattice QCD. Main results in lattice
QCD simulations are given.Comment: 10 pages, 5 figures, Talk at the 5th International Conference on
Computational Physics (ICCP5), 11-13 October, 1999, Kanazawa, to appear in
Prog. Theor. Phys. (Suppl.) No. 138 (2000
Spin, charge and orbital ordering in La0.5Sr1.5MnO4
We have analyzed the experimental evidence of charge and orbital ordering in
La0.5Sr1.5MnO4 using first principles band structure calculations. Our results
suggest the presence of two types of Mn sites in the system. One of the Mn
sites behaves like an Mn(3+) ion, favoring a Jahn-Teller distortion of the
surrounding oxygen atoms, while the distortion around the other is not a simple
breathing mode kind. Band structure effects are found to dominate the
experimental spectrum for orbital and charge ordering, providing an alternate
explanation for the experimentally observed results.Comment: 4 pages + 3 figures; To appear in Phys. Rev. Let
Inverse versus Normal NiAs Structure as High-Pressure Phase of FeO and MnO
The high-pressure phases of FeO and MnO were studied by the first principles
calculations. The present theoretical study predicts that the high-pressure
phase of MnO is a metallic normal B8 structure (nB8), while that of FeO should
take the inverse B8 structure (iB8). The novel feature of the unique
high-pressure phase of stoichiometric FeO is that the system should be a band
insulator in the ordered antiferromagnetic (AF) state and that the existence of
a band gap leads to special stability of the phase. The observed metallicity of
the high-pressure and high-temperature phase of FeO may be caused by the loss
of AF order and also by the itinerant carriers created by non-stoichiometry.
Analysis of x-ray diffraction experiments provides a further support to the
present theoretical prediction for both FeO and MnO. Strong stability of the
high-pressure phase of FeO will imply possible important roles in Earth's core.Comment: 7 pages, 3 figures and 1 table; submitted to "Nature
Lymphoid/nonlymphoid compartmentalization of donor leukocyte chimerism in rat recipients of heart allografts, with or without adjunct bone marrow
Background. The role of leukocyte migration and chimerism in organ allograft acceptance has been obscured by the lack of information about the late localization of the donor cells. Methods. Male Lewis rat→female Brown Norway abdominal heart transplantation was performed under tacrolimus immunosuppression (days 0-13, 20, and 27) with or without donor bone marrow and (in bone marrow subgroups) a 1-week postoperative course of a possibly chimerism-enhancing drug. Using rat sex-determining region-Y-specific oligonucleotide primers, we determined the donor DNA concentration by polymerase chain reaction in serial venous blood sampies for 100 days and in tissue specimens when animals were killed. Results. Chimerism was detected out to 56 days in 89% of the blood samples but in none of the samples at 100 days. However, donor DNA was detected when animals were killed in 95% of the native hearts, 80% of the skin biopsy specimens, and 23% of the spleens. The presence and quantity of early and late chimerism were strongly correlated the administration of adjunct bone marrow and with a reduction in the vasculopathy and inflammation index in the cardiac allografts. Marginally significant further increases in chimerism and/or reductions in chronic heart rejection beyond those achieved with adjunct bone marrow alone were associated with additional treatment with the growth factors Flt-3 ligand, granulocyte colonystimulating factor, and a recombinant molecular variant of interleukin-6 (interleukin-6 mutein) but not with hepatocyte growth factor or lisofylline. Conclusions. The previously suspected shift of early chimerism in the blood and lymphoid organs to dominance in host nonlymphoid tissues is consistent with the dual mechanisms of clonal exhaustion and immune indifference, governed by antigen migration and localization, that have been postulated elsewhere to account for organ allograft acceptance
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