413 research outputs found
The 4-spinon dynamical structure factor of the Heisenberg chain
We compute the exact 4-spinon contribution to the zero-temperature dynamical
structure factor of the spin-1/2 Heisenberg isotropic antiferromagnet in zero
magnetic field, directly in the thermodynamic limit. We make use of the
expressions for matrix elements of local spin operators obtained by Jimbo and
Miwa using the quantum affine symmetry of the model, and of their adaptation to
the isotropic case by Abada, Bougourzi and Si-Lakhal (correcting some overall
factors). The 4-spinon contribution to the first frequency moment sum rule at
fixed momentum is calculated. This shows, as expected, that most of the
remaining correlation weight above the known 2-spinon part is carried by
4-spinon states. Our results therefore provide an extremely accurate
description of the exact structure factor.Comment: 13 page
Pompe disease in children and adults: natural course, disease severity and impact on daily life; results from an international patient survey
Pompe disease is a lysosomal storage disorder caused by deficiency of the enzyme acid alpha-glucosidase and mainly characterized by progressive skeletal muscle weakness. Research on this so far untreatable disease has long been directed towards unraveling the pathophysiological mechanisms and the development of a causal treatment. At the advent of enzyme replacement therapy, the research described in this thesis was intended to include the patientâ €™s perspective in the assessment of the consequences of the disease. The aims were to map out the health status of patients with non- classic or late-onset Pompe disease, to provide more insight in the natural course and rate of progression on a group level, and to evaluate the use of specific self-report measurement scales. These studies form the basis for further follow-up of patients before and after the start of therapy, and are examples of a successful cooperation between patients, patient organizations and universities
How to calculate correlation functions of Heisenberg chains
We describe a method for calculating dynamical spin-spin correlation
functions in the finite isotropic and anisotropic antiferromagnetic Heisenberg
models. Our method is able to produce results with high accuracy over the full
parameter space.Comment: Proceedings of the "Tenth Training Course in the Physics of
Correlated Electron Systems and High-Tc Superconductors", Salerno, Oct 200
Gapped Heisenberg spin chains in a field
We consider the fully anisotropic Heisenberg spin-1/2 antiferromagnet in a
uniform magnetic field, whose ground-state is characterized by broken spin
rotation symmetry and gapped spinon excitations. We expand on a recent
mean-field approach to the problem by incorporating fluctuations in a loop
expansion. Quantitative results for the magnetization, excitation gap and
specific heat are obtained. We compare our predictions with new DMRG and exact
diagonalization data and, for zero field, with the exact solution of the
spin chain from the Bethe Ansatz.Comment: 11 pages, 14 figure
Spectral Properties of Interacting One-Dimensional Spinless Fermions
The spectral properties of the spinless fermion model with nearest-neighbor
repulsive interactions on a one-dimensional lattice are investigated using the
Bethe ansatz. Although its bulk quantities are exactly the same as those of the
spin-1/2 XXZ chain, the difference in the statistics of particles causes
substantial effects on spectral features, such as gapless points of dispersion
relations and line shapes of spectral functions. In this Letter, we clarify the
origin of the differences in spectral features between fermionic and bosonic
systems in terms of Bethe ansatz solutions. We also confirm that the two-string
solutions have considerable spectral weights in the high-energy regime.Comment: 4 pages, 2 figure
The Multimodality Treatment of Rectal Cancer
The aim of this thesis is to further improve the multimodality treatment for rectal cancer, locally advanced rectal cancer and locally recurrent rectal cance
- …