Reconstructing Images from Projections Using the Maximum-Entropy Method. Numerical Simulations of Low-Aspect Astrotomography

The reconstruction of images from a small number of projections using the maximum-entropy method (MEM) with the Shannon entropy is considered. MEM provides higher-quality image reconstruction for sources with extended components than the Hogbom CLEAN method, which is also used in low-aspect astrotomography. The quality of image reconstruction for sources with mixed structure containing bright, compact features embedded in a comparatively weak, extended base can be further improved using a difference-mapping method, which requires a generalization of MEM for the reconstruction of sign-variable functions.We draw conclusions based on the results of numerical simulations for a number of model radio sources with various morphologies.Comment: 11 pages, 9 figure

ATPγS stalls splicing after B complex formation but prior to spliceosome activation.

The ATP analog ATPγS inhibits pre-mRNA splicing in vitro, but there have been conflicting reports as to which step of splicing is inhibited by this small molecule and its inhibitory mechanism remains unclear. Here we have dissected the effect of ATPγS on pre-mRNA splicing in vitro. Addition of ATPγS to splicing extracts depleted of ATP inhibited both catalytic steps of splicing. At ATPγS concentrations ≥0.5 mM, precatalytic B complexes accumulate, demonstrating a block prior to or during the spliceosome activation stage. Affinity purification of the ATPγS-stalled B complexes (B(ATPγS)) and subsequent characterization of their abundant protein components by 2D gel electrophoresis revealed that B(ATPγS) complexes are compositionally more homogeneous than B complexes previously isolated in the presence of ATP. In particular, they contain little or no Prp19/CDC5L complex proteins, indicating that these proteins are recruited after assembly of the precatalytic spliceosome. Under the electron microscope, B(ATPγS) complexes exhibit a morphology highly similar to B complexes, indicating that the ATPγS-induced block in the transformation of the B to B(act) complex is not due to a major structural defect. Likely mechanisms whereby ATPγS blocks spliceosome assembly at the activation stage, including inhibition of the RNA helicase Brr2, are discussed. Given their more homogeneous composition, B complexes stalled by ATPγS may prove highly useful for both functional and structural analyses of the precatalytic spliceosome and its conversion into an activated B(act) spliceosomal complex

Invariant description of solutions of hydrodynamic type systems in hodograph space: hydrodynamic surfaces

Hydrodynamic surfaces are solutions of hydrodynamic type systems viewed as non-parametrized submanifolds of the hodograph space. We propose an invariant differential-geometric characterization of hydrodynamic surfaces by expressing the curvature form of the characteristic web in terms of the reciprocal invariants.Comment: 12 page

Laplace transformations of hydrodynamic type systems in Riemann invariants: periodic sequences

The conserved densities of hydrodynamic type system in Riemann invariants satisfy a system of linear second order partial differential equations. For linear systems of this type Darboux introduced Laplace transformations, generalising the classical transformations in the scalar case. It is demonstrated that Laplace transformations can be pulled back to the transformations of the corresponding hydrodynamic type systems. We discuss periodic Laplace sequences of with the emphasize on the simplest nontrivial case of period 2. For 3-component systems in Riemann invariants a complete discription of closed quadruples is proposed. They turn to be related to a special quadratic reduction of the (2+1)-dimensional 3-wave system which can be reduced to a triple of pairwize commuting Monge-Ampere equations. In terms of the Lame and rotation coefficients Laplace transformations have a natural interpretation as the symmetries of the Dirac operator, associated with the (2+1)-dimensional n-wave system. The 2-component Laplace transformations can be interpreted also as the symmetries of the (2+1)-dimensional integrable equations of Davey-Stewartson type. Laplace transformations of hydrodynamic type systems originate from a canonical geometric correspondence between systems of conservation laws and line congruences in projective space.Comment: 22 pages, Late

Identification of a small molecule inhibitor that stalls splicing at an early step of spliceosome activation.

Small molecule inhibitors of pre-mRNA splicing are important tools for identifying new spliceosome assembly intermediates, allowing a finer dissection of spliceosome dynamics and function. Here, we identified a small molecule that inhibits human pre-mRNA splicing at an intermediate stage during conversion of pre-catalytic spliceosomal B complexes into activated Bact complexes. Characterization of the stalled complexes (designated B028) revealed that U4/U6 snRNP proteins are released during activation before the U6 Lsm and B-specific proteins, and before recruitment and/or stable incorporation of Prp19/CDC5L complex and other Bact complex proteins. The U2/U6 RNA network in B028 complexes differs from that of the Bact complex, consistent with the idea that the catalytic RNA core forms stepwise during the B to Bact transition and is likely stabilized by the Prp19/CDC5L complex and related proteins. Taken together, our data provide new insights into the RNP rearrangements and extensive exchange of proteins that occurs during spliceosome activation

Algebraic varieties in Birkhoff strata of the Grassmannian Gr(2)\mathrm{^{(2)}}: Harrison cohomology and integrable systems

Local properties of families of algebraic subsets $W_g$ in Birkhoff strata $\Sigma_{2g}$ of Gr$^{(2)}$ containing hyperelliptic curves of genus $g$ are studied. It is shown that the tangent spaces $T_g$ for $W_g$ are isomorphic to linear spaces of 2-coboundaries. Particular subsets in $W_g$ are described by the intergrable dispersionless coupled KdV systems of hydrodynamical type defining a special class of 2-cocycles and 2-coboundaries in $T_g$. It is demonstrated that the blows-ups of such 2-cocycles and 2-coboundaries and gradient catastrophes for associated integrable systems are interrelated.Comment: 28 pages, no figures. Generally improved version, in particular the Discussion section. Added references. Corrected typo

The low-temperature sol-gel synthesis of metal-oxide films on polymer substrates and the determination of their optical and dielectric properties

Photoactive, optically transparent heterostructures from silver nanowires and titanium dioxide were obtained by the sol-gel method on the surface of a polyethylene terephthalate film. The characteristics of optical transmission on the wavelength and those of dielectric permittivity, conductivity and dissipation on frequency in the range of 25–1,000,000 Hz were investigated

Far-infrared vibrational properties of linear C60 polymers: A comparison between neutral and charged materials

We report the far-infrared transmittance spectrum of a pure phase of the orthorhombic high-temperature and high-pressure C-60 polymer and compare the results with a previously published spectrum of the charged RbC60 orthorhombic polymer. Assignments for both spectra are made with the aid of first-principles quantum molecular dynamics simulations of the two materials. We find that the striking spectral differences between the neutral and charged linear fullerene polymers can be fully accounted for by charge effects on the C-60 ball

New Superhard Phases for 3D C60-based Fullerites

We have explored new possible phases of 3D C60-based fullerites using semiempirical potentials and ab-initio density functional methods. We have found three closely related structures - two body centered orthorhombic and one body centered cubic - having 52, 56 and 60 tetracoordinated atoms per molecule. These 3D polymers result in semiconductors with bulk moduli near 300 GPa, and shear moduli around 240 GPa, which make them good candidates for new low density superhard materials.Comment: To be published in Physical Review Letter

Highly Effective xMAP Multiplex Assay for the Detection and Identification of Hemorrhagic Fever Agents, Including Ebola Virus

Developed has been the oligonucleotide liquid biochip based on xMAP technology, designed for the laboratory detection of particularly dangerous viral pathogens such as Ebola and Marburg filoviruses, and Machupo , Junin, and Lassa arenaviruses. The suggested approach allows for the detection of up to 100 viral genome equivalents in a sample. The sensitivity and specificity of oligonucleotide biochip is 100 % when the laboratory panels of positive and negative samples are used. These results indicate that the xMAP multiplexing for the detection and identification of tropical hemorrhagic fever agents, including Ebola virus, is not inferior to the conventional method such as real-time RT-PCR and can be applied for evaluation of viral load, and further on can easily be expanded for both the analysis of new viral agents and for the detection of critical mutations in viral genomes