Drinfeld second realization of the quantum affine superalgebras of D(1)(2,1;x)D^{(1)}(2,1;x) via the Weyl groupoid

We obtain Drinfeld second realization of the quantum affine superalgebras associated with the affine Lie superalgebra $D^{(1)}(2,1;x)$. Our results are analogous to those obtained by Beck for the quantum affine algebras. Beck's analysis uses heavily the (extended) affine Weyl groups of the affine Lie algebras. In our approach the structures are based on a Weyl groupoid.Comment: 40 pages, 1 figure. close to the final version to appear in RIMS Kokyuroku Bessatsu (Besstsu) B8 (2008) 171-21

The table mountain 8-mm-wavelength interferometer

The system components, performance, and calibration of two element radio interferometer operating at 8.33 mm wavelength are discussed. The interferometer employs a 5.5 m and a 3 m diameter antenna on an east-west baseline of 60 or 120 m, yielding fringe spacings at transit of 28 or 14 in. respectively. The broad intermediate frequency bandpass of 100 to 350 MHz and the system noise temperature of 500 K provide high sensitivity for the measurement of continuum sources. The interferometer has been used for high resolution studies of the planets and the Sun, and it is currently being adapted to study solar flare emissions at high spatial and time resolution

Pressure-induced phase transition and bi-polaronic sliding in a hole-doped Cu_2O_3 ladder system

We study a hole-doped two-leg ladder system including metal ions, oxygen, and electron-lattice interaction, as a model for Sr_{14-x}Ca_xCu_{24}O_{41-\delta}. Single- and bi-polaronic states at 1/4-hole doping are modeled as functions of pressure by applying an unrestricted Hartree-Fock approximation to a multiband Peierls-Hubbard Hamiltonian. We find evidence for a pressure-induced phase transition between single-polaron and bi-polaron states. The electronic and phononic excitations in those states, including distinctive local lattice vibrational modes, are calculated by means of a direct-space Random Phase approximation. Finally, as a function of pressure, we identify a transition between site- and bond-centered bi-polarons, accompanied by a soft mode and a low-energy charge-sliding mode. We suggest comparisons with available experimented data

Jacobson generators of the quantum superalgebra Uq[sl(n+1∣m)]U_q[sl(n+1|m)] and Fock representations

As an alternative to Chevalley generators, we introduce Jacobson generators for the quantum superalgebra $U_q[sl(n+1|m)]$. The expressions of all Cartan-Weyl elements of $U_q[sl(n+1|m)]$ in terms of these Jacobson generators become very simple. We determine and prove certain triple relations between the Jacobson generators, necessary for a complete set of supercommutation relations between the Cartan-Weyl elements. Fock representations are defined, and a substantial part of this paper is devoted to the computation of the action of Jacobson generators on basis vectors of these Fock spaces. It is also determined when these Fock representations are unitary. Finally, Dyson and Holstein-Primakoff realizations are given, not only for the Jacobson generators, but for all Cartan-Weyl elements of $U_q[sl(n+1|m)]$.Comment: 27 pages, LaTeX; to be published in J. Math. Phy

Avalanche Dynamics in Wet Granular Materials

We have studied the dynamics of avalanching wet granular media in a rotating drum apparatus. Quantitative measurements of the flow velocity and the granular flux during avalanches allow us to characterize novel avalanche types unique to wet media. We also explore the details of viscoplastic flow (observed at the highest liquid contents) in which there are lasting contacts during flow, leading to coherence across the entire sample. This coherence leads to a velocity independent flow depth at high rotation rates and novel robust pattern formation in the granular surface.Comment: 5 pages, 3 figures in color, REVTeX4, for smaller pdfs see http://angel.elte.hu/~tegzes/condmat.htm

Genome-Wide Studies of Histone Demethylation Catalysed by the Fission Yeast Homologues of Mammalian LSD1

In order to gain a more global view of the activity of histone demethylases, we report here genome-wide studies of the fission yeast SWIRM and polyamine oxidase (PAO) domain homologues of mammalian LSD1. Consistent with previous work we find that the two S. pombe proteins, which we name Swm1 and Swm2 (after SWIRM1 and SWIRM2), associate together in a complex. However, we find that this complex specifically demethylates lysine 9 in histone H3 (H3K9) and both up- and down-regulates expression of different groups of genes. Using chromatin-immunoprecipitation, to isolate fragments of chromatin containing either H3K4me2 or H3K9me2, and DNA microarray analysis (ChIP-chip), we have studied genome-wide changes in patterns of histone methylation, and their correlation with gene expression, upon deletion of the swm1+ gene. Using hyper-geometric probability comparisons we uncover genetic links between lysine-specific demethylases, the histone deacetylase Clr6, and the chromatin remodeller Hrp1. The data presented here demonstrate that in fission yeast the SWIRM/PAO domain proteins Swm1 and Swm2 are associated in complexes that can remove methyl groups from lysine 9 methylated histone H3. In vitro, we show that bacterially expressed Swm1 also possesses lysine 9 demethylase activity. In vivo, loss of Swm1 increases the global levels of both H3K9me2 and H3K4me2. A significant accumulation of H3K4me2 is observed at genes that are up-regulated in a swm1 deletion strain. In addition, H3K9me2 accumulates at some genes known to be direct Swm1/2 targets that are down-regulated in the swm1¿ strain. The in vivo data indicate that Swm1 acts in concert with the HDAC Clr6 and the chromatin remodeller Hrp1 to repress gene expression. In addition, our in vitro analyses suggest that the H3K9 demethylase activity requires an unidentified post-translational modification to allow it to act. Thus, our results highlight complex interactions between histone demethylase, deacetylase and chromatin remodelling activities in the regulation of gene expression

Finite-dimensional representations of the quantum superalgebra Uq[gl(n/m)]U_q[gl(n/m)] and related q-identities

Explicit expressions for the generators of the quantum superalgebra $U_q[gl(n/m)]$ acting on a class of irreducible representations are given. The class under consideration consists of all essentially typical representations: for these a Gel'fand-Zetlin basis is known. The verification of the quantum superalgebra relations to be satisfied is shown to reduce to a set of $q$-number identities.Comment: 12 page

Structure of the string R-matrix

By requiring invariance directly under the Yangian symmetry, we rederive Beisert's quantum R-matrix, in a form that carries explicit dependence on the representation labels, the braiding factors, and the spectral parameters u_i. In this way, we demonstrate that there exist a rewriting of its entries, such that the dependence on the spectral parameters is purely of difference form. Namely, the latter enter only in the combination u_1-u_2, as indicated by the shift automorphism of the Yangian. When recasted in this fashion, the entries exhibit a cleaner structure, which allows to spot new interesting relations among them. This permits to package them into a practical tensorial expression, where the non-diagonal entries are taken care by explicit combinations of symmetry algebra generators.Comment: 9 pages, LaTeX; typos correcte