806 research outputs found
Relative replication capacity of phenotypic SIV variants during primary infections differs with route of inoculation
BACKGROUND: Previous studies of human and simian immunodeficiency virus (HIV and SIV) have demonstrated that adaptive mutations selected during the course of infection alter viral replicative fitness, persistence, and pathogenicity. What is unclear from those studies is the impact of transmission on the replication and pathogenicity of the founding virus population. Using the SIV-macaque model, we examined whether the route of infection would affect the establishment and replication of two SIVmne variants of distinct in vitro and in vivo biological characteristics. For these studies, we performed dual-virus inoculations of pig-tailed macaques via intrarectal or intravenous routes with SIVmneCl8, a miminally pathogenic virus, and SIVmne027, a highly pathogenic variant that replicates more robustly in CD4(+ )T cells. RESULTS: The data demonstrate that SIVmne027 is the dominant virus regardless of the route of infection, indicating that the capacity to replicate efficiently in CD4(+ )T cells is important for fitness. Interestingly, in comparison to intravenous co-infection, intrarectal inoculation enabled greater relative replication of the less pathogenic virus, SIVmneCl8. Moreover, a higher level of SIVmneCl8 replication during primary infection of the intrarectally inoculated macaques was associated with lower overall plasma viral load and slower decline in CD4(+ )T cells, even though SIVmne027 eventually became the dominant virus. CONCLUSIONS: These results suggest that the capacity to replicate in CD4(+ )T cells is a significant determinant of SIV fitness and pathogenicity. Furthermore, the data also suggest that mucosal transmission may support early replication of phenotypically diverse variants, while slowing the rate of CD4(+ )T cell decline during the initial stages of infection
Phase Diagram of Pressure-Induced Superconductivity in EuFe2As2 Probed by High-Pressure Resistivity up to 3.2 GPa
We have constructed a pressuretemperature () phase diagram of
-induced superconductivity in EuFeAs single crystals, via
resistivity () measurements up to 3.2 GPa. As hydrostatic pressure is
applied, an antiferromagnetic (AF) transition attributed to the FeAs layers at
shifts to lower temperatures, and the corresponding resistive
anomaly becomes undetectable for 2.5 GPa. This suggests that the
critical pressure where becomes zero is about 2.5
GPa. We have found that the AF order of the Eu moments survives up to
3.2 GPa without significant changes in the AF ordering temperature
. The superconducting (SC) ground state with a sharp transition
to zero resistivity at 30 K, indicative of bulk
superconductivity, emerges in a pressure range from 2.5
GPa to 3.0 GPa. At pressures close to but outside the SC phase, the
curve shows a partial SC transition (i.e., zero resistivity is not
attained) followed by a reentrant-like hump at approximately
with decreasing temperature. When nonhydrostatic pressure with a uniaxial-like
strain component is applied using a solid pressure medium, the partial
superconductivity is continuously observed in a wide pressure range from 1.1
GPa to 3.2 GPa.Comment: 7 pages, 6 figures, accepted for publication in Physical Review B,
selected as "Editors' Suggestion
Detection of the interfacial exchange field at a ferromagnetic insulator-nonmagnetic metal interface with pure spin currents
At the interface between a nonmagnetic metal (NM) and a ferromagnetic
insulator (FI) spin current can interact with the magnetization, leading to a
modulation of the spin current. The interfacial exchange field at these FI-NM
interfaces can be probed by placing the interface in contact with the spin
transport channel of a lateral spin valve (LSV) device and observing additional
spin relaxation processes. We study interfacial exchange field in lateral spin
valve devices where Cu spin transport channel is in proximity with
ferromagnetic insulator EuS (EuS-LSV) and yttrium iron garnet
YFeO (YIG-LSV). The spin signals were compared with reference
lateral spin valve devices fabricated on nonmagnetic Si/SiO substrate with
MgO or AlO capping. The nonlocal spin valve signal is about 4 and 6 times
lower in the EuS-LSV and YIG-LSV, respectively. The suppression in the spin
signal has been attributed to enhanced surface spin-flip probability at the
Cu-EuS (or Cu-YIG) interface due to interfacial spin-orbit field. Besides spin
signal suppression we also found widely observed low temperature peak in the
spin signal at 30 K is shifted to higher temperature in the case of
devices in contact with EuS or YIG. Temperature dependence of spin signal for
different injector-detector distances reveal fluctuating exchange field at
these interfaces cause additional spin decoherence which limit spin relaxation
time in addition to conventional sources of spin relaxation. Our results show
that temperature dependent measurement with pure spin current can be used to
probe interfacial exchange field at the ferromagnetic insulator-nonmagnetic
metal interface.Comment: 10 pages, 3 figures, accepted in Physical Review
Quasi-Two-Dimensional Fermi Surfaces and Coherent Interlayer Transport in KFeAs
We report the results of the angular-dependent magnetoresistance oscillations
(AMROs), which can determine the shape of bulk Fermi surfaces in
quasi-two-dimensional (Q2D) systems, in a highly hole-doped Fe-based
superconductor KFeAs with 3.7 K. From the AMROs, we
determined the two Q2D FSs with rounded-square cross sections, corresponding to
12% and 17% of the first Brillouin zone. The rounded-squared shape of the FS
cross section is also confirmed by the analyses of the interlayer transport
under in-plane fields. From the obtained FS shape, we infer the character of
the 3d orbitals that contribute to the FSs.Comment: 4 pages, 4 figures, accepted in Phys. Rev. Let
High-Pressure Electrical Resistivity Measurements of EuFe2As2 Single Crystals
High-pressure electrical resistivity measurements up to 3.0GPa have been
performed on EuFe2As2 single crystals with residual resistivity ratios RRR=7
and 15. At ambient pressure, a magnetic / structural transition related to
FeAs-layers is observed at T0 =190K and 194K for samples with RRR=7 and 15,
respectively. Application of hydrostatic pressure suppresses T0, and then
induces similar superconducting behavior in the samples with different RRR
values. However, the critical pressure 2.7GPa, where T0=0, for the samples with
RRR=15 is slightly but distinctly larger than 2.5GPa for the samples with
RRR=7.Comment: To be published in J. Phys.: Conf. Se
Quantum oscillations in a centrosymmetric skyrmion-hosting magnet GdRu2Si2
We have performed magnetic torque and resistivity measurements on a
centrosymmetric skyrmion-host GdRu2Si2, in which the dominant magnetic
interaction leading to skyrmion formation is under debate. We observe both the
de Haas-van Alphen and Shubnikov-de Haas oscillations in the forced
ferromagnetic phase. The angular dependence of the quantum oscillation
frequencies can be reproduced by the ab-initio calculation. The de Haas-van
Alphen oscillation is also observed in the double-Q phase with a different
frequency to that in the forced ferromagnetic phase, indicating a Fermi surface
reconstruction due to the coupling between localized spins and conduction
electrons. Based on these experimental findings, the magnetic interactions in
this system are discussed.Comment: 11 pages, 8 figure
The Competition between Staggered Field and Antiferromagnetic Interactions in Cugeo3:Fe
The EPR spectra along different crystallographic axes for single crystals of
CuGeO3 containing 1% of Fe impurity have been studied in the frequency range
60-360 GHz at temperatures 0.5-30 K. The analysis based on the Oshikawa-Affleck
(OA) theory suggests that the temperature dependences of the line width and
g-factor are formed as a result of the competition between interchain
antiferromagnetic interactions and staggered Zeeman energy. It is found that
staggered magnetic moments in CuGeO3:Fe are located predominantly along b axis.Comment: 9 pages, 4 figures; submitted to QSS04 symposiu
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