8,802 research outputs found
High-Frequency Spin Waves in YBa2Cu3O6.15
Pulsed neutron spectroscopy is used to make absolute measurements of the
dynamic magnetic susceptibility of insulating YBa2Cu3O6.15. Acoustic and
optical modes, derived from in- and out-of-phase oscillation of spins in
adjacent CuO2 planes, dominate the spectra and are observed up to 250 meV. The
optical modes appear first at 74 meV. Linear-spin-wave theory gives an
excellent description of the data and yields intra- and inter-layer exchange
constants of J_parallel =125 meV and J_perp = 11 meV respectively and a
spin-wave intensity renormalization Z_chi = 0.4.Comment: postscript, 11 pages, 4 figures, Fig.2 fixe
Simulating adiabatic evolution of gapped spin systems
We show that adiabatic evolution of a low-dimensional lattice of quantum
spins with a spectral gap can be simulated efficiently. In particular, we show
that as long as the spectral gap \Delta E between the ground state and the
first excited state is any constant independent of n, the total number of
spins, then the ground-state expectation values of local operators, such as
correlation functions, can be computed using polynomial space and time
resources. Our results also imply that the local ground-state properties of any
two spin models in the same quantum phase can be efficiently obtained from each
other. A consequence of these results is that adiabatic quantum algorithms can
be simulated efficiently if the spectral gap doesn't scale with n. The
simulation method we describe takes place in the Heisenberg picture and does
not make use of the finitely correlated state/matrix product state formalism.Comment: 13 pages, 2 figures, minor change
NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures
Long-range magnetic interactions in highly magnetised liquids
(laser-polarised 3He-4He dilute mixtures at 1 K in our experiment) introduce a
significant non-linear and non-local contribution to the evolution of nuclear
magnetisation that leads to instabilities during free precession. We recently
demonstrated that a multi-echo NMR sequence, based on the magic sandwich pulse
scheme developed for solid-state NMR, can be used to stabilise the
magnetisation against the effect of distant dipolar fields. Here, we report
investigations of echo attenuation in an applied field gradient that show the
potential of this NMR sequence for spin diffusion measurements at high
magnetisation densities.Comment: Accepted for publication in the Journal of Low Temperature Physic
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Tumor necrosis factor-alpha regulates the expression of inducible costimulator receptor ligand on CD34+ progenitor cells during differentiation into antigen presenting cells
The inducible costimulator receptor (ICOS) is a third member of the CD28 receptor family that regulates T cell activation and function. ICOS binds to a newly identified ligand on antigen presenting cells different from the CD152 ligands CD80 and CD86. We used soluble ICOSIg and a newly developed murine anti-human ICOS ligand (ICOSL) monoclonal antibody to further characterize the ICOSL during ontogeny of antigen presenting cells. In a previous study, we found that ICOSL is expressed on monocytes, dendritic cells, and B cells. To define when ICOSL is first expressed on myeloid antigen presenting cells, we examined ICOSL expression on CD34 cells in bone marrow. We found that CD34bright cells regardless of their myeloid commitment were ICOSL , whereas ICOSL was first expressed when CD34 expression diminished and the myeloid marker CD33 appeared
Plans for a Neutron EDM Experiment at SNS
The electric dipole moment of the neutron, leptons, and atoms provide a
unique window to Physics Beyond the Standard Model. We are currently developing
a new neutron EDM experiment (the nEDM Experiment). This experiment, which will
be run at the 8.9 A Neutron Line at the Fundamental Neutron Physics Beamline
(FNPB) at the Spallation Neutron Source (SNS) at the Oak Ridge National
Laboratory, will search for the neutron EDM with a sensitivity two orders of
magnitude better than the present limit. In this paper, the motivation for the
experiment, the experimental method, and the present status of the experiment
are discussed.Comment: 9 Pages, 4 Figures, submitted to the proceedings of the Second
Meeting of the APS Topical Group on Hadronic Physics, Nashville, TN, October
22-24, 200
Comment on ``Measurement of the He mass diffusion coefficient in superfluid He over the 0.45--0.95 K temperature range
The role of 3He-3He collisions in our diffusion experiment is addressed and
shown to not be relevant to the measurement of 3He diffusion against phonons in
superfluid helium.Comment: Two pages, in Europhysics Letters forma
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