Quantum freeze of fidelity decay for chaotic dynamics

We show that the mechanism of quantum freeze of fidelity decay for perturbations with a zero time average, recently discovered for a specific case of integrable dynamics [New J. Phys. 5, 109 (2003)], can be generalized to arbitrary quantum dynamics. We work out explicitly the case of a chaotic classical counterpart, for which we find semiclassical expressions for the value and the range of the plateau of fidelity. After the plateau ends, we find explicit expressions for the asymptotic decay, which can be exponential or Gaussian depending on the ratio of the Heisenberg time to the decay time. Arbitrary initial states can be considered; e.g., we discuss coherent states and random states.     

A general method for alkylating 2(5H)-furanones; reduction of products to 3-, 2,3-, and 3,4-substituted furans

The cycloaddition of diazoalkanes, diazoesters and diazoketones to 2(5H)-furanones followed by thermal decomposition of the respective adducts is shown to provide a general method for the preparation of a variety of alkylated 2(5H)-furanones. Reduction of the latter compounds with diisobutylaluminum hydride affords the corresponding substituted furans in good yield.     

Determination of some ampholytic and cationic surfactants by potentiometric titrations based on ion-pair formation

Ampholytic surfactants of the betaine type are titrated directly with sodium tetraphenylborate in acidic medium, in which they become cationic forms. Generally, ampholytic surfactants and cationic surfactants that contain hydrophilic groups can be determined by precipitation with sodium tetraphenylborate, the excess of which is back-titrated with thallium(I) nitrate. An aluminium wire electrode coated with a plasticized PVC membrane is used for end-point indication. Characteristic data are given for determinations of nine surfactants and applications to textiles are outlined.     

Characterizing graph drawing with eigenvectors

Two definitions of the problem of graph drawing are considered, and an analytical solution is provided for each of them. The solutions obtained make use of the eigenvectors of the Laplacian matrix of a related structure. The procedures give good results for symmetrical graphs, and they have already been used for drawing fullerene molecules in the literature. The analysis characterizes precisely what problems the two procedures are solving. It also illuminates why they can perform unsatisfactorily on asymmetrical graphs.     

How to compute the Wiener index of a graph

The Wiener index of a graphG is equal to the sum of distances between all pairs of vertices ofG. It is known that the Wiener index of a molecular graph correlates with certain physical and chemical properties of a molecule. In the mathematical literature, many good algorithms can be found to compute the distances in a graph, and these can easily be adapted for the calculation of the Wiener index. An algorithm that calculates the Wiener index of a tree in linear time is given. It improves an algorithm of Canfield, Robinson and Rouvray. The question remains: is there an algorithm for general graphs that would calculate the Wiener index without calculating the distance matrix? Another algorithm that calculates this index for an arbitrary graph is given.     

Conformational analysis—133: 3,3-dimethyl-2,4-pentanedione. The importance of induction and solvationTetrahedron 34, 3385 (1978).

The conformations of the title compound have been analyzed in detail with respect to steric interaction energies, charge interaction energies, and solvation energies in heptane and benzene. Using previously developed methods, which include induction by dipoles in polarizable bonds, and the solvation of molecular dipoles and quadrupoles, predictions regarding the conformational equilibrium are made. These were tested by experimental determination of the dipole moment of the molecule in heptane and benzene, and are in agreement with the predictions. More simplified calculations lead to qualitatively erroneous results.     

On representation of DNA by line distance matrix

Recently Line Distance (LD) matrix has been introduced as a novel route for characterization of DNA sequences. The approach was based on construction of four separate submatrices for the four nucleotides, the first row of each of which records the separation between the selected nucleotide and the remaining nucleotides of the same kind. In this article, we consider an alternative representation of DNA by LD matrix in which we construct a single matrix for each DNA sequence. The approach is illustrated on the DNA sequence of the first exon of human β-globin gene.     

Plastic Stress Distribution in a Rotating Disk with Rigid Inclusion Under a Radial Temperature Gradient∗

Abstract

This study investigates the plastic stress distribution in a rotating disk with rigid inclusion, under an axially symmetric steady-state temperature gradient. The analysis is based on Tresca's yield condition, its associated flow rule, and linear strain hardening material behavior.

     

G-Quadruplex Aptamer-Ligand Characterization

In this work we explore the structure of a G-rich DNA aptamer termed AT11-L2 (TGGTGGTGGTTGTTGTTGGTGGTGGTGGT; derivative of AT11) by evaluating the formation and stability of G-quadruplex (G4) conformation under different experimental conditions such as KCl concentration, temperature, and upon binding with a variety of G4 ligands (360A, BRACO-19, PDS, PhenDC3, TMPyP4). We also determined whether nucleolin (NCL) can be a target of AT11-L2 G4. Firstly, we assessed by circular dichroism, UV and NMR spectroscopies the formation of G4 by AT11-L2. We observed that, for KCl concentrations of 65 mM or less, AT11-L2 adopts hybrid or multiple topologies. In contrast, a parallel topology predominates for buffer containing 100 mM of KCl. The T_m of AT11-L2 in 100 mM of KCl is 38.9 °C, proving the weak stability of this sequence. We also found that upon titration with two molar equivalents of 360A, BRACO-19 and PhenDC3, the G4 is strongly stabilized and its topology is maintained, while the addition of 3.5 molar equivalents of TMPyP4 promotes the disruption of G4. The K_D values between AT11-L2 G4, ligands and NCL were obtained by fluorescence titrations and are in the range of µM for ligand complexes and nM when adding NCL. In silico studies suggest that four ligands bind to the AT11-L2 G4 structure by stacking interactions, while the RBD1,2 domains of NCL interact preferentially with the thymines of AT11-L2 G4. Finally, AT11-L2 G4 co-localized with NCL in NCL-positive tongue squamous cell carcinoma cell line.