1,615 research outputs found
Ultrasonic pole figure for the texture of aluminum alloy
Copyright 1987 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters, 50(20), 1411-1412, 1987 and may be found at http://dx.doi.org/10.1063/1.9783
Discovery of coesite and stishovite in HED meteorite
第3回極域科学シンポジウム/第35回南極隕石シンポジウム 11月29日(木) 国立国語研究所 2階講
Immune Modulation through 4-1BB Enhances SIV Vaccine Protection in Non-Human Primates against SIVmac251 Challenge
Costimulatory molecules play a central role in the development of cellular immunity. Understanding how costimulatory pathways can be directed to positively influence the immune response may be critical for the generation of an effective HIV vaccine. Here, we evaluated the ability of intravenous administration of a blocking monoclonal antibody (mAb) directed against the negative costimulatory molecule CTLA-4, and an agonist mAb directed against the positive costimulatory molecule 4-1BB, either alone or in combination, to augment intramuscular SIV DNA immunizations. We then tested the ability these of these responses to impact a high-dose SIVmac251 challenge. Following immunization, the groups infused with the anti-4-1BB mAb exhibited enhanced IFN-γ responses compared to the DNA vaccine only group. Interestingly, although CTLA-4 blockade alone did not enhance IFN-γ responses it did increase the proliferative capacity of the CD4+ and CD8+ T cells. The combination of both mAbs enhanced the magnitude of the polyfunctional CD8+ T cell response. Following challenge, the group that received both mAbs exhibited a significant, ∼2.0 log, decrease in plasma viral load compared to the naïve group the included complete suppression of viral load in some animals. Furthermore, the use of the CTLA-4 blocking antibody resulted in significantly higher viral loads during chronic infection compared to animals that received the 4-1BB mAb, likely due to the higher CD4+ T cell proliferative responses which were driven by this adjuvant following immunization. These novel studies show that these adjuvants induce differential modulation of immune responses, which have dramatically different consequences for control of SIV replication, suggesting important implications for HIV vaccine development
Pressure Destabilizes Oxygen Vacancies in Bridgmanite
Bridgmanite may contain a large proportion of ferric iron in its crystal structure in the forms of FeFeO3 and MgFeO2.5 components. We investigated the pressure dependence of FeFeO3 and MgFeO2.5 contents in bridgmanite coexisting with MgFe2O4-phase and with or without ferropericlase in the MgO-SiO2-Fe2O3 ternary system at 2,300 K, 33 and 40 GPa. Together with the experiments at 27 GPa reported in Fei et al. (2020, https://doi.org/10.1029/2019GL086296), our results show that the FeFeO3 and MgFeO2.5 contents in bridgmanite decrease from 7.6 to 5.3 mol % and from 2 to 3 mol % to nearly zero, respectively, with increasing pressure from 27 to 40 GPa. Accordingly, the total Fe3+ decreases from 0.18 to 0.11 pfu. The formation of oxygen vacancies (MgFeO2.5 component) in bridgmanite is therefore dramatically suppressed by pressure. Oxygen vacancies can be produced by ferric iron in Fe3+-rich bridgmanite under the topmost lower mantle conditions, but the concentration should decrease rapidly with increasing pressure. The variation of oxygen-vacancy content with depth may potentially affect the physical properties of bridgmanite and thus affect mantle dynamics
Microlensing Results Challenge the Core Accretion Runaway Growth Scenario for Gas Giants
We compare the planet-to-star mass-ratio distribution measured by
gravitational microlensing to core accretion theory predictions from population
synthesis models. The core accretion theory's runaway gas accretion process
predicts a dearth of intermediate-mass giant planets that is not seen in the
microlensing results. In particular, the models predict fewer
planets at mass ratios of than inferred
from microlensing observations. This tension implies that gas giant formation
may involve processes that have hitherto been overlooked by existing core
accretion models or that the planet-forming environment varies considerably as
a function of host-star mass. Variation from the usual assumptions for the
protoplanetary disk viscosity and thickness could reduce this discrepancy, but
such changes might conflict with microlensing results at larger or smaller mass
ratios, or with other observations. The resolution of this discrepancy may have
important implications for planetary habitability because it has been suggested
that the runaway gas accretion process may have triggered the delivery of water
to our inner solar system. So, an understanding of giant planet formation may
help us to determine the occurrence rate of habitable planets.Comment: 12 pages, 2 figures, 1 table, accepted for publication in ApJ
Self-Diffusion of a Polymer Chain in a Melt
Self-diffusion of a polymer chain in a melt is studied by Monte Carlo
simulations of the bond fluctuation model, where only the excluded volume
interaction is taken into account. Polymer chains, each of which consists of
segments, are located on an simple cubic lattice
under periodic boundary conditions, where each segment occupies unit cells. The results for
and 512 at the volume fraction are reported, where
for and L=192 for . The -dependence of the
self-diffusion constant is examined. Here, is estimated from the mean
square displacements of the center of mass of a single polymer chain at the
times larger than the longest relaxation time. From the data for , 384
and 512, the apparent exponent , which describes the apparent power
law dependence of on as , is estimated as
. The ratio seems to be a
constant for and 512, where and
denote the longest relaxation time and the mean square end-to-end distance,
respectively.Comment: 4 pages, 3 figures, submitted to J. Phys. Soc. Jp
Structural stability of Fe5Si3 and Ni2Si studied by high-pressure x-ray diffraction and ab initio total-energy calculations
We performed high-pressure angle dispersive x-ray diffraction measurements on
Fe5Si3 and Ni2Si up to 75 GPa. Both materials were synthesized in bulk
quantities via a solid-state reaction. In the pressure range covered by the
experiments, no evidence of the occurrence of phase transitions was observed.
On top of that, Fe5Si3 was found to compress isotropically, whereas an
anisotropic compression was observed in Ni2Si. The linear incompressibility of
Ni2Si along the c-axis is similar in magnitude to the linear incompressibility
of diamond. This fact is related to the higher valence-electron charge density
of Ni2Si along the c-axis. The observed anisotropic compression of Ni2Si is
also related to the layered structure of Ni2Si where hexagonal layers of Ni2+
cations alternate with graphite-like layers formed by (NiSi)2- entities. The
experimental results are supported by ab initio total-energy calculations
carried out using density functional theory and the pseudopotential method. For
Fe5Si3, the calculations also predicted a phase transition at 283 GPa from the
hexagonal P63/mcm phase to the cubic structure adopted by Fe and Si in the
garnet Fe5Si3O12. The room-temperature equations of state for Fe5Si3 and Ni2Si
are also reported and a possible correlation between the bulk modulus of iron
silicides and the coordination number of their minority element is discussed.
Finally, we report novel descriptions of these structures, in particular of the
predicted high-pressure phase of Fe5Si3 (the cation subarray in the garnet
Fe5Si3O12), which can be derived from spinel Fe2SiO4 (Fe6Si3O12).Comment: 44 pages, 13 figures, 3 Table
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