3,072 research outputs found
Mesencephalic dopamine neurons regulate the expression of neuropeptide mRNAs in the rat forebrain.
The susceptibility and excitation spectrum of (VO)PO in ladder and dimer chain models
We present numerical results for the magnetic susceptibility of a Heisenberg
antiferromagnetic spin ladder, as a function of temperature and the spin-spin
interaction strengths and . These are contrasted with new
bulk limit results for the dimer chain. A fit to the experimental
susceptibility of the candidate spin-ladder compound vanadyl pyrophosphate,
(VO)PO, gives the parameters meV and meV. With these values we predict a singlet-triplet energy gap of
meV, and give a numerical estimate of the ladder triplet
dispersion relation . In contrast, a fit to the dimer chain model
leads to meV and meV, which predicts a gap of meV.Comment: 16 pages, 6 figures available upon request, RevTex 3.0, preprint
ORNL-CCIP-94-04 / RAL-94-02
Two-stage spin-flop transitions in S = 1/2 antiferromagnetic spin chain BaCu_2Si_2O_7
Two-stage spin-flop transitions are observed the in quasi-one-dimensional
antiferromagnet, BaCuSiO. A magnetic field applied along the
easy axis induces a spin-flop transition at 2.0 T followed by a second
transition at 4.9 T. The magnetic susceptibility indicates the presence of
Dzyaloshinskii-Moriya (DM) antisymmetric interactions between the intrachain
neighboring spins. We discuss a possible mechanism whereby the geometrical
competition between DM and interchain interactions, as discussed for the
two-dimensional antiferromagnet LaCuO, causes the two-stage
spin-flop transitions.Comment: 5 pages, 3 figures (included), accepted for publication in Phys. Rev.
Let
Weak ferromagnetism of quasi-one-dimensional S=1/2 antiferromagnet BaCuGeO
Weak ferromagnetism of quasi-one-dimensional S = 1/2 antiferromagnet
BaCuGeO is studied by the magnetization measurement. The
spontaneous magnetization appears along the b axis. The local symmetry between
the in-chain nearest neighbor spins allows the presence of
Dzyaloshinskii-Moriya interaction, and the only possible spatial configuration
of the weak ferromagnetic moment per spin determines the sign of the
inter-chain interaction. A weak -axis magnetic field can change the
direction of the magnetization to the -axis direction, which shows that the
spin chain forms a weakly coupled weak-ferromagnetic chain system.Comment: 10 pages, 4 figure
Susceptibility of the Spin 1/2 Heisenberg Antiferromagnetic Chain
Highly accurate results are presented for the susceptibility, of
the Heisenberg antiferromagnetic chain for all temperatures, using the
Bethe ansatz and field theory methods. After going through a rounded peak,
approaches its asympotic zero-temperature value with infinite slope.Comment: 8 pages and 3 postscript figures appended (uuencoded), Revtex, Report
#:UBCTP-94-00
Correlation amplitude for S=1/2 XXZ spin chain in the critical region
The density-matrix renormalization-group technique is used to calculate the
spin correlation functions and of the one-dimensional
S=1/2 XXZ model in the gapless regime. The numerical results for open chains of
200 spins are analyzed by comparing them with correlation functions calculated
from a low-energy field theory. This gives precise estimates of the amplitudes
of the correlation functions in the thermodynamic limit. The exact amplitude
recently conjectured by Lukyanov and Zamolodchikov and the logarithmic
correction in the Heisenberg model are confirmed numerically.Comment: 4 pages, 3 figures, final versio
Magnetic phase diagram and structure of the magnetic phases in the quasi-one-dimensional antiferromagnet BaCu_2Si_2O_7: symmetry analysis
We have performed a symmetry analysis of the properties of the recently
discovered quasi-one-dimensional compound BaCu_2Si_2O_7. The existence of the
unusual spin-reorientation transitions is explained as an effect of the
unusually strong relativistic interactions. The possible connection between the
magnitude of the relativistic interactions and the low-dimensional structure of
the BaCu_2Si_2O_7 is discussed. The structure of the magnetic phases is
determined.Comment: REVTEX, 8 pages, 4 Figires V3: misprints fixed, small changes due to
the discussion with PRB refere
From 'River Cottage' to 'Chicken Run': Hugh Fearnley-Whttingstall and the class politics of ethical consumption
Lifestyle television provides a key site through which to explore the dilemmas of ethical consumption, as the genre shifts to consider the ethics of different consumption practices and taste cultures. UK television cook Hugh Fearnley-Whittingstall's TV programmes offer fertile ground not only for thinking about television personalities as lifestyle experts and moral entrepreneurs, but also for thinking about how the meanings and uses of their television image are inflected by genre. In this article we explore how the shift from the lifestyled downshifting narrative of the River Cottage series to the 'campaigning culinary documentary' Hugh's Chicken Run exposes issues of celebrity, class and ethics. While both series are concerned with ethical consumption, they work in different ways to reveal a distinction between 'ethical' and 'unethical' consumption practices and positions - positions that are inevitably classed
Magnetic Properties of (VO)_2P_2O_7 from Frustrated Interchain Coupling
Neutron-scattering experiments on (VO)_2P_2O_7 reveal both a gapped magnon
dispersion and an unexpected, low-lying second mode. The proximity and
intensity of these modes suggest a frustrated coupling between the alternating
spin chains. We deduce the minimal model containing such a frustration, and
show that it gives an excellent account of the magnon dispersion, static
susceptibility and electron spin resonance absorption. We consider two-magnon
states which bind due to frustration, and demonstrate that these may provide a
consistent explanation for the second mode.Comment: RevTeX, 5 pages, 6 figures, compressed from first versio
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