776 research outputs found
On the relation between entanglement and subsystem Hamiltonians
We show that a proportionality between the entanglement Hamiltonian and the
Hamiltonian of a subsystem exists near the limit of maximal entanglement under
certain conditions. Away from that limit, solvable models show that the
coupling range differs in both quantities and allow to investigate the effect.Comment: 7 pages, 2 figures version2: minor changes, typos correcte
Ising films with surface defects
The influence of surface defects on the critical properties of magnetic films
is studied for Ising models with nearest-neighbour ferromagnetic couplings. The
defects include one or two adjacent lines of additional atoms and a step on the
surface. For the calculations, both density-matrix renormalization group and
Monte Carlo techniques are used. By changing the local couplings at the defects
and the film thickness, non-universal features as well as interesting crossover
phenomena in the magnetic exponents are observed.Comment: 8 pages, 12 figures included, submitted to European Physical Journal
Crumpling transition of the triangular lattice without open edges: effect of a modified folding rule
Folding of the triangular lattice in a discrete three-dimensional space is
investigated by means of the transfer-matrix method. This model was introduced
by Bowick and co-workers as a discretized version of the polymerized membrane
in thermal equilibrium. The folding rule (constraint) is incompatible with the
periodic-boundary condition, and the simulation has been made under the
open-boundary condition. In this paper, we propose a modified constraint, which
is compatible with the periodic-boundary condition; technically, the
restoration of translational invariance leads to a substantial reduction of the
transfer-matrix size. Treating the cluster sizes L \le 7, we analyze the
singularities of the crumpling transitions for a wide range of the bending
rigidity K. We observe a series of the crumpling transitions at K=0.206(2),
-0.32(1), and -0.76(10). At each transition point, we estimate the latent heat
as Q=0.356(30), 0.08(3), and 0.05(5), respectively
Reduced density matrix and entanglement entropy of permutationally invariant quantum many-body systems
In this paper we discuss the properties of the reduced density matrix of
quantum many body systems with permutational symmetry and present basic
quantification of the entanglement in terms of the von Neumann (VNE), Renyi and
Tsallis entropies. In particular, we show, on the specific example of the spin
Heisenberg model, how the RDM acquires a block diagonal form with respect
to the quantum number fixing the polarization in the subsystem conservation
of and with respect to the irreducible representations of the
group. Analytical expression for the RDM elements and for the
RDM spectrum are derived for states of arbitrary permutational symmetry and for
arbitrary polarizations. The temperature dependence and scaling of the VNE
across a finite temperature phase transition is discussed and the RDM moments
and the R\'{e}nyi and Tsallis entropies calculated both for symmetric ground
states of the Heisenberg chain and for maximally mixed states.Comment: Festschrift in honor of the 60th birthday of Professor Vladimir
Korepin (11 pages, 5 figures
Qualitative Analysis of Nonlinear Systems by the Lotka-Volterra Approach
In this paper, the authors summarize recent results obtained by applying the Lotka-Volterra approach to problems in nonlinear systems analysis. This approach was developed at the Mathematics and Cybernetics Division of the GDR Academy of Sciences (Berlin); various applications have been investigated in collaboration with the System and Decision Sciences Program at IIASA.
This paper should also be seen as a contribution to the debate on future directions of research at IIASA, in particular possible research into the evolution of macrosystems
Critical behaviour in parabolic geometries
We study two-dimensional systems with boundary curves described by power
laws. Using conformal mappings we obtain the correlations at the bulk critical
point. Three different classes of behaviour are found and explained by scaling
arguments which also apply to higher dimensions. For an Ising system of
parabolic shape the behaviour of the order at the tip is also found.Comment: Old paper, for archiving. 6 pages, 1 figure, epsf, IOP macr
Incommensurate Matrix Product State for Quantum Spin Systems
We introduce a matrix product state (MPS) with an incommensurate periodicity
by applying the spin-rotation operator of each site to a uniform MPS in the
thermodynamic limit. The spin rotations decrease the variational energy with
accompanying translational symmetry breaking and the rotational symmetry
breaking in the spin space even if the Hamiltonian has the both symmetries. The
optimized pitch of rotational operator reflects the commensurate/incommensurate
properties of spin-spin correlation functions in the Heisenberg chain
and the ferro-antiferro zigzag chain.Comment: 6 pages, 5 figure
Psychotic disorder, khat abuse and aggressive behavior in Somalia: a case report
The current literature on khat and mental disorders focuses on khat-induced disorders neglecting at large the adverse consequences of co-morbid use on pre-existing disorders. The case of a 32 year old Somali with a delusional disorder and co-morbid khat abuse is presented who killed a man in the
state of paranoid delusions. The psychotic exacerbation prior to this incident was accompanied by an increase of khat intake. Co-morbid khat abuse can lead to the deterioration of psychotic disorders, can facilitate aggressive acts and complicates treatment. The medical and legal system of the countries
where khat use reaches highest levels are not fully prepared to deal with such cases. Further research and the development of adequate prevention and treatment measures is urgently needed.
KEY WORDS: khat, psychosis, co-morbidity, aggression, Somali
Folding of the triangular lattice in a discrete three-dimensional space: Crumpling transitions in the negative-bending-rigidity regime
Folding of the triangular lattice in a discrete three-dimensional space is
studied numerically. Such ``discrete folding'' was introduced by Bowick and
co-workers as a simplified version of the polymerized membrane in thermal
equilibrium. According to their cluster-variation method (CVM) analysis, there
appear various types of phases as the bending rigidity K changes in the range
-infty < K < infty. In this paper, we investigate the K<0 regime, for which the
CVM analysis with the single-hexagon-cluster approximation predicts two types
of (crumpling) transitions of both continuous and discontinuous characters. We
diagonalized the transfer matrix for the strip widths up to L=26 with the aid
of the density-matrix renormalization group. Thereby, we found that
discontinuous transitions occur successively at K=-0.76(1) and -0.32(1).
Actually, these transitions are accompanied with distinct hysteresis effects.
On the contrary, the latent-heat releases are suppressed considerably as
Q=0.03(2) and 0.04(2) for respective transitions. These results indicate that
the singularity of crumpling transition can turn into a weak-first-order type
by appreciating the fluctuations beyond a meanfield level
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