175,906 research outputs found
Some Recent Results on Pair Correlation Functions and Susceptibilities in Exactly Solvable Models
Using detailed exact results on pair-correlation functions of Z-invariant
Ising models, we can write and run algorithms of polynomial complexity to
obtain wavevector-dependent susceptibilities for a variety of Ising systems.
Reviewing recent work we compare various periodic and quasiperiodic models,
where the couplings and/or the lattice may be aperiodic, and where the Ising
couplings may be either ferromagnetic, or antiferromagnetic, or of mixed sign.
We present some of our results on the square-lattice fully-frustrated Ising
model. Finally, we make a few remarks on our recent works on the pentagrid
Ising model and on overlapping unit cells in three dimensions and how these
works can be utilized once more detailed results for pair correlations in,
e.g., the eight-vertex model or the chiral Potts model or even
three-dimensional Yang-Baxter integrable models become available.Comment: LaTeX2e using iopart.cls, 10 pages, 5 figures (5 eps files), Dunk
Island conference in honor of 60th birthday of A.J. Guttman
aFold – using polynomial uncertainty modelling for differential gene expression estimation from RNA sequencing data
Data normalization and identification of significant differential expression represent crucial steps in RNA-Seq analysis. Many available tools rely on assumptions that are often not met by real data, including the common assumption of symmetrical distribution of up- and down-regulated genes, the presence of only few differentially expressed genes and/or few outliers. Moreover, the cut-off for selecting significantly differentially expressed genes for further downstream analysis often depend on arbitrary choices
Effective models for gapped phases of strongly correlated quantum lattice models
We present a robust scheme to derive effective models non-perturbatively for
quantum lattice models when at least one degree of freedom is gapped. A
combination of graph theory and the method of continuous unitary
transformations (gCUTs) is shown to efficiently capture all zero-temperature
fluctuations in a controlled spatial range. The gCUT can be used either for
effective quasi-particle descriptions or for effective low-energy descriptions
in case of infinitely degenerate subspaces. We illustrate the method for 1d and
2d lattice models yielding convincing results in the thermodynamic limit. We
find that the recently discovered spin liquid in the Hubbard model on the
honeycomb lattice lies outside the perturbative strong-coupling regime. Various
extensions and perspectives of the gCUT are discussed.Comment: 6 pages, 5 figures, extended discussion on J2/J1 for the honeycomb
Hubbard model and on the properties of different generators for the
continuous unitary transformatio
New structural approach for determining load carrying capability of filament wound composite materials
Metal lined boron and graphite composites exhibit high strength and minimum weight, making them superior to aluminum cylindrical shell structures and to steel or aluminum constructed pressure vessels. S glass filament-epoxy resin matrix with aluminum liner is suitable for cryogenic tanks
Cluster magnetic fields from active galactic nuclei
Active galactic nuclei (AGN) found at the centers of clusters of galaxies are
a possible source for weak cluster-wide magnetic fields. To evaluate this
scenario, we present 3D adaptive mesh refinement MHD simulations of a cool-core
cluster that include injection of kinetic, thermal, and magnetic energy via an
AGN-powered jet. Using the MHD solver in FLASH 2, we compare several
sub-resolution approaches that link the estimated accretion rate as measured on
the simulation mesh to the accretion rate onto the central black hole and the
resulting feedback. We examine the effects of magnetized outflows on the
accretion history of the black hole and discuss the ability of these models to
magnetize the cluster medium.Comment: 4 pages, 2 figures, submitted to conference proceedings "The
Monster's Fiery Breath: Feedback in Groups, Galaxies, and Clusters
The Influence of AGN Feedback on Galaxy Cluster Observables
Galaxy clusters are valuable cosmological probes. However, cluster mass
estimates rely on observable quantities that are affected by complicated
baryonic physics in the intracluster medium (ICM), including feedback from
active galactic nuclei (AGN). Cosmological simulations have started to include
AGN feedback using subgrid models. In order to make robust predictions, the
systematics of different implementations and parametrizations need to be
understood. We have developed an AGN subgrid model in FLASH that supports a few
different black hole accretion models and feedback models. We use this model to
study the effect of AGN on X-ray cluster observables and its dependence on
model variations.Comment: minor error corrected, to appear in proceedings of the conference
"The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters",
June 2009, Madison, Wisconsi
Optical properties of 4 A single-walled carbon nanotubes inside the zeolite channels studied from first principles calculations
The structural, electronic, and optical properties of 4 A single-walled
carbon nanotubes (SWNTs) contained inside the zeolite channels have been
studied based upon the density-functional theory in the local-density
approximation (LDA). Our calculated results indicate that the relaxed
geometrical structures for the smallest SWNTs in the zeolite channels are much
different from those of the ideal isolated SWNTs, producing a great effect on
their physical properties. It is found that all three kinds of 4 A SWNTs can
possibly exist inside the Zeolite channels. Especially, as an example, we have
also studied the coupling effect between the ALPO_4-5 zeolite and the tube
(5,0) inside it, and found that the zeolite has real effects on the electronic
structure and optical properties of the inside (5,0) tube.Comment: 9 pages, 6figure
Coronal magnetic fields produced by photospheric shear
The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear, by a simple functional form
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