31,358 research outputs found
Nuclear Spin-Lattice Relaxation in One-Dimensional Heisenberg Ferrimagnets: Three-Magnon versus Raman Processes
Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is
studied by means of a modified spin-wave theory. We consider the second-order
process, where a nuclear spin flip induces virtual spin waves which are then
scattered thermally via the four-magnon exchange interaction, as well as the
first-order process, where a nuclear spin directly interacts with spin waves
via the hyperfine interaction. We point out a possibility of the three-magnon
relaxation process predominating over the Raman one and suggest model
experiments.Comment: to be published in J. Phys. Soc. Jpn. 73, No. 6 (2004
Elementary Excitations of Heisenberg Ferrimagnetic Spin Chains
We numerically investigate elementary excitations of the Heisenberg
alternating-spin chains with two kinds of spins 1 and 1/2 antiferromagnetically
coupled to each other. Employing a recently developed efficient Monte Carlo
technique as well as an exact diagonalization method, we verify the spin-wave
argument that the model exhibits two distinct excitations from the ground state
which are gapless and gapped. The gapless branch shows a quadratic dispersion
in the small-momentum region, which is of ferromagnetic type. With the
intention of elucidating the physical mechanism of both excitations, we make a
perturbation approach from the decoupled-dimer limit. The gapless branch is
directly related to spin 1's, while the gapped branch originates from
cooperation of the two kinds of spins.Comment: 7 pages, 7 Postscript figures, RevTe
Modified spin-wave theory of nuclear magnetic relaxation in one-dimensional quantum ferrimagnets: Three-magnon versus Raman processes
Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is
studied by means of a modified spin-wave theory. Calculating beyond the
first-order mechanism, where a nuclear spin directly interacts with spin waves
through the hyperfine coupling, we demonstrate that the
exchange-scattering-enhanced three-magnon nuclear relaxation may generally
predominate over the Raman one with increasing temperature and decreasing
field. Recent proton spin-lattice relaxation-time (T_1_) measurements on the
ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O suggest
that the major contribution to 1/T_1_ be made by the three-magnon scattering.Comment: 8 pages, 5 figure
Ground State Property of an Alternating Spin Ladder Involving Two Kinds of Inter-Chain Interactions
The ground state property of the alternating spin ladder is studied in the
case that the system involves an antiferromagnetic intra-chain interaction as
well as two kinds of inter-chain interactions; one is between spins of the same
magnitude and the other is between spins with different magnitudes. The
calculation has been carried out by the exact diagonalization method. As a
consequence of the competition among interactions, the system is revealed to
show an interesting variety of phases in the ground state property. Its phase
diagram is exhibited in the parameter space of the system. We find that,
however small the total amount of the inter-chain interactions is, the
ferrimagnetic ground state becomes unstable in a certain region. In this case,
which of the ferrimagnetic and the singlet ground state to appear is determined
only by the ratio between the inter-chain interactions regardless of their
total amount. The nature of two phases appearing in the singlet region of the
phase diagram and the type of the phase transition between them are also
discussed. The results are ensured by comparing with those of obtained in other
models which are contained in our model as special limiting cases.Comment: 12 pages, 9 PostScript figure
On the phase transition of light in cavity QED lattices
Systems of strongly interacting atoms and photons, that can be realized
wiring up individual cavity QED systems into lattices, are perceived as a new
platform for quantum simulation. While sharing important properties with other
systems of interacting quantum particles here we argue that the nature of
light-matter interaction gives rise to unique features with no analogs in
condensed matter or atomic physics setups. By discussing the physics of a
lattice model of delocalized photons coupled locally with two-level systems
through the elementary light-matter interaction described by the Rabi model, we
argue that the inclusion of counter rotating terms, so far neglected, is
crucial to stabilize finite-density quantum phases of correlated photons out of
the vacuum, with no need for an artificially engineered chemical potential. We
show that the competition between photon delocalization and Rabi non-linearity
drives the system across a novel parity symmetry-breaking quantum
criticality between two gapped phases which shares similarities with the Dicke
transition of quantum optics and the Ising critical point of quantum magnetism.
We discuss the phase diagram as well as the low-energy excitation spectrum and
present analytic estimates for critical quantities.Comment: 5+3 pages, published versio
-- coupling in He with the Nijmegen soft-core potentials
The -- coupling in
He is studied with the [ + +
] + [ + + ] + [ + + ] model,
where the particle is assumed as a frozen core. We use the Nijmegen
soft-core potentials, NSC97e and NSC97f, for the valence baryon-baryon part,
and the phenomenological potentials for the parts (=,
, and ). We find that the calculated of He for NSC97e and NSC97f are,
respectively, 0.6 and 0.4 MeV in the full coupled-channel calculation, the
results of which are about half in comparison with the experimental data,
MeV.
Characteristics of the sector in the NSC97 potentials are discussed in
detail.Comment: 18 pages, 4 figure
Low-Energy Structure of Heisenberg Ferrimagnetic Spin Chains
Static and dynamic structure factors of Heisenberg ferrimagnetic spin chains
are numerically investigated. There exist two distinct branches of elementary
excitations, which exhibit ferromagnetic and antiferromagnetic aspects. The
ferromagnetic feature is smeared out with the increase of temperature, whereas
the antiferromagnetic one persists up to higher temperatures. The scattering
intensity is remarkably large at lower boundaries of the ferromagnetic and
antiferromagnetic spectra. All these observations are consistent with the
ferromagnetic-to-antiferromagnetic crossover in the thermal behavior which has
recently been reported.Comment: 3 pages, 5 PS figures, to appear in J. Phys. Soc. Jpn. Vol. 67, No.
11 (1998
Mapping of Mature and Young Oil Palm Distributions in a Humid Tropical River Basin for Flood Vulnerability Assessment
International Conference on the Ocean and Earth Sciences 18-20 November 2020, Jakarta Selatan, IndonesiaOil palm is one of the key drivers of economic growth in some regions in the humid tropical countries such as Indonesia. Previous studies show that floods risk at particular river basins in Indonesia will increase in the future due to climate change. This will give negative impacts to the sustainable production of palm oil in the future and subsequently the regions' economy. Discussion on adaptation strategies on this matter is necessary however, the vulnerability of oil palm plantations against floods at river basin scale are still poorly understood. Field surveys for oil palms' vulnerability at such scale is costly in time, labour and resources, and making use of remote sensing is more feasible. The aim of this study is to use remote sensing in assessing oil palm vulnerability against floods at river basin scale. To achieve this objective two oil palm distribution maps which were developed using Sentinel imageries for years 2015 and 2018 allowing young oil palms to be matured under normal condition. To understand the impact of floods to oil palms, a composite of flood extents using radar scenes for years 2016 and 2017 was developed. Our results show that young oil palms are highly vulnerable to floods compared to matured ones. Only 6% of the earlier could survived floods and be matured in time, while most of the matured ones could survive
Nuclear Magnetic Relaxation in the Ferrimagnetic Chain Compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O: Three-Magnon Scattering?
Recent proton spin-lattice relaxation-time (T_1_) measurements on the
ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O are
explained by an elaborately modified spin-wave theory. We give a strong
evidence of the major contribution to 1/T_1_ being made by the three-magnon
scattering rather than the Raman one.Comment: J. Phys.: Condens. Matter 16, No. 49, 9023 (2004
- …