465 research outputs found
Exact ground states for two new spin-1 quantum chains, new features of matrix product states
We use the matrix product formalism to find exact ground states of two new
spin-1 quantum chains with nearest neighbor interactions. One of the models,
model I, describes a one-parameter family of quantum chains for which the
ground state can be found exactly. In certain limit of the parameter, the
Hamiltonian turns into the interesting case . The other model which we label as model II, corresponds to a
family of solvable three-state vertex models on square two dimensional
lattices. The ground state of this model is highly degenerate and the matrix
product states is a generating state of such degenerate states. The simple
structure of the matrix product state allows us to determine the properties of
degenerate states which are otherwise difficult to determine. For both models
we find exact expressions for correlation functions.Comment: 22 pages, references added, accepted for publication in European
Physics Journal
The square-kagome quantum Heisenberg antiferromagnet at high magnetic fields: The localized-magnon paradigm and beyond
We consider the spin-1/2 antiferromagnetic Heisenberg model on the
two-dimensional square-kagome lattice with almost dispersionless lowest magnon
band. For a general exchange coupling geometry we elaborate low-energy
effective Hamiltonians which emerge at high magnetic fields. The effective
model to describe the low-energy degrees of freedom of the initial frustrated
quantum spin model is the (unfrustrated) square-lattice spin-1/2 model in
a -aligned magnetic field. For the effective model we perform quantum Monte
Carlo simulations to discuss the low-temperature properties of the
square-kagome quantum Heisenberg antiferromagnet at high magnetic fields. We
pay special attention to a magnetic-field driven
Berezinskii-Kosterlitz-Thouless phase transition which occurs at low
temperatures.Comment: 6 figure
Entanglement and quantum phase transitions in matrix product spin one chains
We consider a one-parameter family of matrix product states of spin one
particles on a periodic chain and study in detail the entanglement properties
of such a state. In particular we calculate exactly the entanglement of one
site with the rest of the chain, and the entanglement of two distant sites with
each other and show that the derivative of both these properties diverge when
the parameter of the states passes through a critical point. Such a point
can be called a point of quantum phase transition, since at this point, the
character of the matrix product state which is the ground state of a
Hamiltonian, changes discontinuously. We also study the finite size effects and
show how the entanglement depends on the size of the chain. This later part is
relevant to the field of quantum computation where the problem of initial state
preparation in finite arrays of qubits or qutrits is important. It is also
shown that entanglement of two sites have scaling behavior near the critical
point
Phase diagram of the asymmetric tetrahedral Ising-Heisenberg chain
The asymmetric tetrahedron is composed by all edges of tetrahedron
represented by Ising interaction except one, which has a Heisenberg type
interaction. This asymmetric tetrahedron is arranged connecting a vertex which
edges are only Ising type interaction to another vertex with same structure of
another tetrahedron. The process is replicated and this kind of lattice we call
the asymmetric Ising-Heisenberg chain. We have studied the ground state phase
diagram for this kind of models. Particularly we consider two situations in the
Heisenberg-type interaction, (i) The asymmetric tetrahedral spin(1/2,1/2)
Ising-XYZ chain, and (ii) the asymmetric tetrahedral spin-(1/2,1) Ising-XXZ
chain, where we have found a rich phase diagram and a number of multicritical
points. Additionally we have also studied their thermodynamics properties and
the correlation function, using the decorated transformation. We have mapped
the asymmetric tetrahedral Ising-Heisenberg chain in an effective Ising chain,
and we have also concluded that it is possible to evaluate the partition
function including a longitudinal external magnetic field.Comment: 14 pages, 8 figures. Accepted in Journal of Physics: Condensed Matte
Mixed Heisenberg Chains. I. The Ground State Problem
We consider a mechanism for competing interactions in alternating Heisenberg
spin chains due to the formation of local spin-singlet pairs. The competition
of spin-1 and spin-0 states reveals hidden Ising symmetry of such alternating
chains.Comment: 7 pages, RevTeX, 4 embedded eps figures, final versio
Stochastic Models on a Ring and Quadratic Algebras. The Three Species Diffusion Problem
The stationary state of a stochastic process on a ring can be expressed using
traces of monomials of an associative algebra defined by quadratic relations.
If one considers only exclusion processes one can restrict the type of algebras
and obtain recurrence relations for the traces. This is possible only if the
rates satisfy certain compatibility conditions. These conditions are derived
and the recurrence relations solved giving representations of the algebras.Comment: 12 pages, LaTeX, Sec. 3 extended, submitted to J.Phys.
A compact and light-weight refractive telescope for the observation of extensive air showers
A general purpose instrument for imaging of Cherenkov light or fluorescence
light emitted by extensive air showers is presented. Its refractive optics
allows for a compact and light-weight design with a wide field-of-view of
12{\deg}. The optical system features a 0.5 m diameter Fresnel lens and a
camera with 61 pixels composed of Winston cones and large-sized 6x6 mm photo
sensors. As photo sensors, semi conductor light sensors (SiPMs) are utilized.
The camera provides a high photon detection efficiency together with robust
operation. The enclosed optics permit operation in regions of harsh
environmental conditions. The low price of the telescope allows the production
of a large number of telescopes and the application of the instrument in
various projects, such as FAMOUS for the Pierre Auger Observatory, HAWC's Eye
for HAWC or IceAct for IceCube. In this paper the novel design of this
telescope and first measurements are presented.Comment: Submitted to JINST, second (minor) revisio
Matrix Product Ground States for Asymmetric Exclusion Processes with Parallel Dynamics
We show in the example of a one-dimensional asymmetric exclusion process that
stationary states of models with parallel dynamics may be written in a matrix
product form. The corresponding algebra is quadratic and involves three
different matrices. Using this formalism we prove previous conjectures for the
equal-time correlation functions of the model.Comment: LaTeX, 8 pages, one postscript figur
Impact of brief prewarming on anesthesia-related core-temperature drop, hemodynamics, microperfusion and postoperative ventilation in cytoreductive surgery of ovarian cancer: a randomized trial
Background: General (GA)- and epidural-anesthesia may cause a drop in body-core-temperature (BCT(drop)), and hypothermia, which may alter tissue oxygenation (StO(2)) and microperfusion after cytoreductive surgery for ovarian cancer. Cell metabolism of subcutaneous fat- or skeletal muscle cells, measured in microdialysis, may be affected. We hypothesized that forced-air prewarming during epidural catheter placement and induction of GA maintains normothermia and improves microperfusion. Methods: After ethics approval 47 women scheduled for cytoreductive surgery were prospectively enrolled. Women in the study group were treated with a prewarming of 43 °C during epidural catheter placement. BCT (Spot on®, 3 M) was measured before (T(1)), after induction of GA (T(2)) at 15 min (T(3)) after start of surgery, and until 2 h after ICU admission (T(ICU2h)). Primary endpoint was BCT(drop) between T(1) and T(2). Microperfusion-, hemodynamic- and clinical outcomes were defined as secondary outcomes. Statistical analysis used the Mann-Whitney-U- and non-parametric-longitudinal tests. Results: BCT(drop) was 0.35 °C with prewarming and 0.9 °C without prewarming (p < 0.005) and BCT remained higher over the observation period (ΔT(4) = 0.9 °C up to ΔT(7) = 0.95 °C, p < 0.001). No significant differences in hemodynamic parameters, transfusion, arterial lactate and dCO(2) were measured. In microdialysis the ethanol ratio was temporarily, but not significantly, reduced after prewarming. Lactate, glucose and glycerol after PW tended to be more constant over the entire period. Postoperatively, six women without prewarming, but none after prewarming were mechanical ventilated (p < 0.001). Conclusion: Prewarming at 43 °C reduces the BCT(drop) and maintains normothermia without impeding the perioperative routine patient flow. Microdialysis indicate better preserved parameters of microperfusion. Trial registration: ClinicalTrials.gov; ID: NCT02364219; Date of registration: 18-febr-2015
Linear independence of localized magnon states
At the magnetic saturation field, certain frustrated lattices have a class of
states known as "localized multi-magnon states" as exact ground states. The
number of these states scales exponentially with the number of spins and
hence they have a finite entropy also in the thermodynamic limit
provided they are sufficiently linearly independent. In this article we present
rigorous results concerning the linear dependence or independence of localized
magnon states and investigate special examples. For large classes of spin
lattices including what we called the orthogonal type and the isolated type as
well as the kagom\'{e}, the checkerboard and the star lattice we have proven
linear independence of all localized multi-magnon states. On the other hand the
pyrochlore lattice provides an example of a spin lattice having localized
multi-magnon states with considerable linear dependence.Comment: 23 pages, 6 figure
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