27,850 research outputs found
Spin-Hall and Anisotropic Magnetoresistance in Ferrimagnetic Co-Gd / Pt layers
We present the Co-Gd composition dependence of the spin-Hall
magnetoresistance (SMR) and anisotropic magnetoresistance (AMR) for
ferrimagnetic Co100-xGdx / Pt bilayers. With Gd concentration x, its magnetic
moment increasingly competes with the Co moment in the net magnetization. We
find a nearly compensated ferrimagnetic state at x = 24. The AMR changes sign
from positive to negative with increasing x, vanishing near the magnetization
compensation. On the other hand, the SMR does not vary significantly even where
the AMR vanishes. These experimental results indicate that very different
scattering mechanisms are responsible for AMR and SMR. We discuss a possible
origin for the alloy composition dependence.Comment: 31 Pages, 9 figure
Causality Violations in Cascade Models of Nuclear Collisions
Transport models have successfully described many aspects of intermediate
energy heavy-ion collision dynamics. As the energies increase in these models
to the ultrarelativistic regime, Lorentz covariance and causality are not
strictly respected. The standard argument is that such effects are not
important to final results; but they have not been seriously considered at high
energies. We point out how and why these happen, how serious of a problem they
may be and suggest ways of reducing or eliminating the undesirable effects.Comment: RevTeX, 23 pages, 9 (uuencoded) figures; to appear in Phys. Rev
Erythropoietin production by fetal mouse liver cells in response to hypoxia and adenylate cyclase stimulation
This study was done to investigate aspects of control of extrarenal erythropoietin (Ep) production. To this end we studied the effects of three stimuli of renal Ep production in the adult, i.e. hypoxia, cobalt, and activation of adenylate cyclase on Ep generation by cultured fetal mouse liver cells. The fetal liver was taken as a model for extrarenal Ep production because this organ is considered the predominant site of extrarenal Ep production. We found that Ep production by the cells increased as the oxygen concentration was decreased in the incubation atmosphere from 20% to 1%. Cobalt (10(-4)-10(-5) M) had no effect on Ep production. Activation of adenylate cyclase by forskolin (10(-5) M) or isoproterenol (10(-5) M) greatly enhanced Ep production. These findings indicate that the Ep-stimulating effect of cobalt is specific for the kidney. However, oxygen depletion and activation of adenylate cyclase seem to be more general stimuli in Ep-producing cells. Furthermore we found that Ep production in hypoxia correlated with lactate formation in the cultured liver cells. This finding suggests that Ep production in fetal livers under hypoxic conditions parallels the shift from aerobic to anaerobic cellular energy metabolism
Superconducting Niobium Accelerator Structures for a Proton Linear Accelerator from 200 to 600 MeV
Spatially resolved ultrafast precessional magnetization reversal
Spatially resolved measurements of quasi-ballistic precessional magnetic
switching in a microstructure are presented. Crossing current wires allow
detailed study of the precessional switching induced by coincident longitudinal
and transverse magnetic field pulses. Though the response is initially
spatially uniform, dephasing occurs leading to nonuniformity and transient
demagnetization. This nonuniformity comes in spite of a novel method for
suppression of end domains in remanence. The results have implications for the
reliability of ballistic precessional switching in magnetic devices.Comment: 17 pages (including 4 figures), submitted to Phys. Rev. Let
Temperatures of Fragment Kinetic Energy Spectra
Multifragmentation reactions without large compression in the initial state
(proton-induced reactions, reverse-kinematics, projectile fragmentation) are
examined, and it is verified quantitatively that the high temperatures obtained
from fragment kinetic energy spectra and lower temperatures obtained from
observables such as level population or isotope ratios can be understood in a
common framework.Comment: LaTeX, 7 pages, 2 figures available from autho
Resistance noise in spin valves
Fluctuations of the magnetization in spin valves are shown to cause
resistance noise that strongly depends on the magnetic configuration. Due to
the applied external field and the dynamic exchange interaction through the
normal metal spacer, the electrical noise level of the antiparallel
configuration can exceed that of the parallel one by an order of magnitude, in
agreement with recent experimental results.Comment: 4 pages, 2 figure
The Resummed Photon Spectrum in Radiative Upsilon Decays
We present a theoretical prediction for the photon spectrum in radiative
Upsilon decay including the effects of resumming the endpoint region, E_\gamma
-> M_\Upsilon/2. Our approach is based on NRQCD and the soft collinear
effective theory. We find that our results give much better agreement with data
than the leading order NRQCD prediction.Comment: 4 pages, 6 figure
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