945 research outputs found
Quasiperiodic Hubbard chains
Low energy properties of half-filled Fibonacci Hubbard models are studied by
weak coupling renormalization group and density matrix renormalization group
method. In the case of diagonal modulation, weak Coulomb repulsion is
irrelevant and the system behaves as a free Fibonacci chain, while for strong
Coulomb repulsion, the charge sector is a Mott insulator and the spin sector
behaves as a uniform Heisenberg antiferromagnetic chain. The off-diagonal
modulation always drives the charge sector to a Mott insulator and the spin
sector to a Fibonacci antiferromagnetic Heisenberg chain.Comment: 4 pages, 4 figures; Final version to appear in Phys. Rev. Let
Critical Properties of the transition between the Haldane phase and the large-D phase of the spin-1/2 ferromagnetic-antiferromagnetic Heisenberg chain with on-site anisotropy"
We analytically study the ground-state quantum phase transition between the
Haldane phase and the large- (LD) phase of the
ferromagnetic-antiferromagnetic alternating Heisenberg chain with on-site
anisotropy. We transform this model into a generalized version of the
alternating antiferromagnetic Heisenberg model with anisotropy. In the
transformed model, the competition between the transverse and longitudinal bond
alternations yields the Haldane-LD transition. Using the bosonization method,
we show that the critical exponents vary continuously on the Haldane-LD
boundary. Our scaling relations between critical exponents very well explains
the numerical results by Hida.Comment: text 12 pages (Plain TeX), LaTeX sourse files of a table and a figure
on reques
Computing automorphic forms on Shimura curves over fields with arbitrary class number
We extend methods of Greenberg and the author to compute in the cohomology of
a Shimura curve defined over a totally real field with arbitrary class number.
Via the Jacquet-Langlands correspondence, we thereby compute systems of Hecke
eigenvalues associated to Hilbert modular forms of arbitrary level over a
totally real field of odd degree. We conclude with two examples which
illustrate the effectiveness of our algorithms.Comment: 15 pages; final submission to ANTS I
Quantum Antiferromagnetism in Quasicrystals
The antiferromagnetic Heisenberg model is studied on a two-dimensional
bipartite quasiperiodic lattice. The distribution of local staggered magnetic
moments is determined on finite square approximants with up to 1393 sites,
using the Stochastic Series Expansion Quantum Monte Carlo method. A non-trivial
inhomogeneous ground state is found. For a given local coordination number, the
values of the magnetic moments are spread out, reflecting the fact that no two
sites in a quasicrystal are identical. A hierarchical structure in the values
of the moments is observed which arises from the self-similarity of the
quasiperiodic lattice. Furthermore, the computed spin structure factor shows
antiferromagnetic modulations that can be measured in neutron scattering and
nuclear magnetic resonance experiments.
This generic model is a first step towards understanding magnetic
quasicrystals such as the recently discovered Zn-Mg-Ho icosahedral structure.Comment: RevTex, 4 pages with 5 figure
Pelatihan terhadap Keterampilan Kader Posyandu
Permasalahan yang diteliti adalah adakah perbedaan keterampilan kader posyandu dalam pengukuran antropometri sebelum dan sesudah pelatihan. Tujuan penelitian ini adalah untuk mengetahui perbedaan keterampilan kader posyandu dalam pengukuran antropometri sebelum dan sesudah pelatihan di wilayah kerja Puskesmas Tarub, Kabupaten Tegal. Metode penelitian menggunakan eksperimen semu dengan rancangan one group pre dan post test design. Sampel berjumlah 25 kader posyandu. Variabel yang diteliti yaitu keterampilan kader sebelum dan sesudah intervensi. Skor keterampilan diukur dua kali yaitu pretest dan posttest. Hasil penelitian menunjukkan dengan uji wilcoxon diperoleh nilai p= 0,0001. Nilai (p<0,05) berarti ada perbedaan yang bermakna dari nilai keterampilan pada saat pretest dan posttest. Hal ini berarti menunjukkan ada perbedaan keterampilan kader posyandu dalam pengukuran antropometri sebelum dan sesudah pelatihan di wilayah kerja Puskesmas Tarub, Kabupaten Tegal. Simpulan penelitian adalah ada perbedaan keterampilan kader posyandu dalam pengukuran antropometri sebelum dan sesudah pelatihan.Research problem was diference of skill posyandu cadres in anthropometric measurements before and after training. Purpose of this study was to determine diferences in skill posyandu cadres in anthropometric measurement before and after training in the working area Tarub Health Center, Tegal District. Research method used quasi-experimental design with one group pre and post test design. Samples were amount of 25 cadres. Variable studied was the skills of cadres before and after training. Scores skills measured by twice pretest and posttest. Test statistic obtained by Wilcoxon test was p value=0,0001. It showed the value <0,05 then there was a significant difference from the values of skills at pretest and posttest. There was difference in skills of posyandu cadres on anthropometric measurement before and after training in the working area Tarub Health Center, Tegal district. Conclusion, there was difference in skills of posyandu cadres on anthropometric measurements before and after training
Interacting Boson Theory of the Magnetization Process of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain
The low temperature magnetization process of the
ferromagnetic-antiferromagnetic Heisenberg chain is studied using the
interacting boson approximation. In the low field regime and near the
saturation field, the spin wave excitations are approximated by the
function boson gas for which the Bethe ansatz solution is available. The finite
temperature properties are calculated by solving the integral equation
numerically. The comparison is made with Monte Carlo calculation and the limit
of the applicability of the present approximation is discussed.Comment: 4 pages, 7 figure
Excitation Spectrum of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain:
The natural explanation of the excitation spectrum of the spin-1
antiferromagnetic Heisenberg chain is given from the viewpoint of the spin-1/2
ferromagnetic-antiferromagnetic alternating Heisenberg chain. The energy
spectrum of the latter is calculated with fixed momentum by numerical
diagonalization of finite size systems. It consists of a branch of propagating
triplet pair (triplet wave) and the continuum of multiple triplet waves for
weak ferromagnetic coupling. As the ferromagnetic coupling increases, the
triplet wave branch is absorbed in the continuum for small , reproducing the
characteristics of the spin-1 antiferromagnetic Heisenberg chain.Comment: 12 Pages REVTEX, Postscript file for the figures included.
SKPH-94-C00
Spectral stochastic processes arising in quantum mechanical models with a non-L2 ground state
A functional integral representation is given for a large class of quantum
mechanical models with a non--L2 ground state. As a prototype the particle in a
periodic potential is discussed: a unique ground state is shown to exist as a
state on the Weyl algebra, and a functional measure (spectral stochastic
process) is constructed on trajectories taking values in the spectrum of the
maximal abelian subalgebra of the Weyl algebra isomorphic to the algebra of
almost periodic functions. The thermodynamical limit of the finite volume
functional integrals for such models is discussed, and the superselection
sectors associated to an observable subalgebra of the Weyl algebra are
described in terms of boundary conditions and/or topological terms in the
finite volume measures.Comment: 15 pages, Plain Te
Behavior of a frustrated quantum spin chain with bond dimerization
We clarified behavior of the excitation gap in a frustrated S=1/2 quantum
spin chain with bond dimerization by using the numerical diagonalization of
finite systems and a variational approach. The model interpolates between the
independent dimer model and the S=1 spin chain by changing a strength of the
dimerization. The energy gap is minimum at the fully-frustrated point, where a
localized kink and a freely mobile anti-kink govern the low-lying excitations.
Away from the point, a kink and an antikink form a bound state by an effective
triangular potential between them. The consequential gap enhancement and the
localization length of the bound state is obtained exactly in the continuous
limit. The gap enhancement obeys a power law with exponent 2/3. The method and
the obtained results are common to other frustrated double spin-chain systems,
such as the one-dimensional J_1 - J_2 model, or the frustrated ladder model.Comment: 11 pages, REVTeX, 8 figures in eps-fil
Alternating Heisenberg Spin-1/2 Chains in a Transverse Magnetic Field
The ground state phase diagram of the alternating spin-1/2 chains with
anisotropic ferromagnetic coupling under the influence of a symmetry breaking
transverse magnetic field is studied. We have used the exact diagonalization
technique. In the limit where the antiferromagnetic coupling is dominant, we
have identified two Ising-type quantum phase transitions. We have calculated
two critical fields and
, corresponding to the transition between different magnetic
phases of the system. It is found that the intermediate state
() is gapful, describing the stripe-antiferromagnetic
phase.Comment: 6 pages, 7 figure
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