Towards combinatorial invariance for Kazhdan-Lusztig polynomials

Kazhdan-Lusztig polynomials are important and mysterious objects in representation theory. Here we present a new formula for their computation for symmetric groups based on the Bruhat graph. Our approach suggests a solution to the combinatorial invariance conjecture for symmetric groups, a well-known conjecture formulated by Lusztig and Dyer in the 1980s.Comment: 47 pages, comments welcom

Doped Sr2FeIrO6 – phase separation and a Jeff ≠ 0 state for Ir5+

High-resolution synchrotron X-ray and neutron powder diffraction data demonstrate that, in contrast to recent reports, Sr2FeIrO6 adopts an I1 symmetry double perovskite structure with an a–b–c– tilting distortion. This distorted structure does not tolerate cation substitution, with low levels of A-site (Ca, Ba, La) or Fe-site (Ga) substitution leading to separation into two phases: a stoichiometric I1 phase and a cation-substituted, P21/n symmetry, a–a–c+ distorted double perovskite phase. Magnetization, neutron diffraction and 57Fe Mössbauer data show that in common with Sr2FeIrO6, the cation substituted Sr2-xAxFe1-yGayIrO6 phases undergo transitions to type-II antiferromagnetically ordered states at TN ~ 120 K. However, in contrast to stoichiometric Sr2FeIrO6, cation substituted samples exhibit a further magnetic transition at TA ~ 220 K, which corresponds to the ordering of reff ≠ 0 Ir5+ centers in the cation-substituted, P21/n symmetry, double perovskite phases

Structural model for the multisubunit Type IC restriction–modification DNA methyltransferase M.EcoR124I in complex with DNA

Recent publication of crystal structures for the putative DNA-binding subunits (HsdS) of the functionally uncharacterized Type I restriction–modification (R-M) enzymes MjaXIP and MgeORF438 have provided a convenient structural template for analysis of the more extensively characterized members of this interesting family of multisubunit molecular motors. Here, we present a structural model of the Type IC M.EcoR124I DNA methyltransferase (MTase), comprising the HsdS subunit, two HsdM subunits, the cofactor AdoMet and the substrate DNA molecule. The structure was obtained by docking models of individual subunits generated by fold-recognition and comparative modelling, followed by optimization of inter-subunit contacts by energy minimization. The model of M.EcoR124I has allowed identification of a number of functionally important residues that appear to be involved in DNA-binding. In addition, we have mapped onto the model the location of several new mutations of the hsdS gene of M.EcoR124I that were produced by misincorporation mutagenesis within the central conserved region of hsdS, we have mapped all previously identified DNA-binding mutants of TRD2 and produced a detailed analysis of the location of surface-modifiable lysines. The model structure, together with location of the mutant residues, provides a better background on which to study protein–protein and protein–DNA interactions in Type I R-M systems

Structural model for the multisubunit Type IC restriction–modification DNA methyltransferase M.EcoR124I in complex with DNA

Recent publication of crystal structures for the putative DNA-binding subunits (HsdS) of the functionally uncharacterized Type I restriction–modification (R-M) enzymes MjaXIP and MgeORF438 have provided a convenient structural template for analysis of the more extensively characterized members of this interesting family of multisubunit molecular motors. Here, we present a structural model of the Type IC M.EcoR124I DNA methyltransferase (MTase), comprising the HsdS subunit, two HsdM subunits, the cofactor AdoMet and the substrate DNA molecule. The structure was obtained by docking models of individual subunits generated by fold-recognition and comparative modelling, followed by optimization of inter-subunit contacts by energy minimization. The model of M.EcoR124I has allowed identification of a number of functionally important residues that appear to be involved in DNA-binding. In addition, we have mapped onto the model the location of several new mutations of the hsdS gene of M.EcoR124I that were produced by misincorporation mutagenesis within the central conserved region of hsdS, we have mapped all previously identified DNA-binding mutants of TRD2 and produced a detailed analysis of the location of surface-modifiable lysines. The model structure, together with location of the mutant residues, provides a better background on which to study protein–protein and protein–DNA interactions in Type I R-M systems

Accurate measurement of long range proton-carbon scalar coupling constants

The accuracy and ease-of-use of various experimental NMR methods for measuringnJCHvalues is assessed.</p

Parity Violating Measurements of Neutron Densities

Parity violating electron nucleus scattering is a clean and powerful tool for measuring the spatial distributions of neutrons in nuclei with unprecedented accuracy. Parity violation arises from the interference of electromagnetic and weak neutral amplitudes, and the $Z^0$ of the Standard Model couples primarily to neutrons at low $Q^2$. The data can be interpreted with as much confidence as electromagnetic scattering. After briefly reviewing the present theoretical and experimental knowledge of neutron densities, we discuss possible parity violation measurements, their theoretical interpretation, and applications. The experiments are feasible at existing facilities. We show that theoretical corrections are either small or well understood, which makes the interpretation clean. The quantitative relationship to atomic parity nonconservation observables is examined, and we show that the electron scattering asymmetries can be directly applied to atomic PNC because the observables have approximately the same dependence on nuclear shape.Comment: 38 pages, 7 ps figures, very minor changes, submitted to Phys. Rev.