Wave attenuation model for dephasing and measurement of conditional times

Inelastic scattering induces dephasing in mesoscopic systems. An analysis of previous models to simulate inelastic scattering in such systems is presented and a relatively new model based on wave attenuation is introduced. The problem of Aharonov-Bohm (AB) oscillations in conductance of a mesoscopic ring is studied. We show that the conductance is symmetric under flux reversal and the visibility of AB oscillations decays to zero as a function of the incoherence parameter, signaling dephasing. Further the wave attenuation model is applied to a fundamental problem in quantum mechanics, that of the conditional (reflection/transmission) times spent in a given region of space by a quantum particle before scattering off from that region.     

Aromaticity and tautomerism—VI : Application of pseudo base equilibria in resonance energy determinations

Equlibrium constants for the addition of hydroxide ion to isoquinolinium methiodide and 3,4-dihydroisoquinolium methiodide, and methoxide ion to 2-phenylisothiazolium, 2-phenylbenzisothiazolium and 2-phenylisothiazolium methiodides are reported. The results are discussed with reference to the aromatic character of the heteroaromatic systems involved.     

Stereochemical investigation of conjugate additions of carbon- and heteronucleophiles to ring-substituted nitrosocyclohexenes

Intermolecular Michael-type conjugate additions of some in situ-generated ring-substituted nitrosocyclohexenes with both carbon- and heteronucleophiles have been found to be highly stereoselective, leading predominantly (or exclusively) to products resulting from axial attack on a half-chair conformation of the nitrosoalkene substrate.     

Hydration water dynamics in biopolymers from NMR relaxation in the rotating frame

Assuming dipole-dipole interaction as the dominant relaxation mechanism of protons of water molecules adsorbed onto macromolecule (biopolymer) surfaces we have been able to model the dependences of relaxation rates on temperature and frequency. For adsorbed water molecules the correlation times are of the order of 10(-5)s, for which the dispersion region of spin-lattice relaxation rates in the rotating frame R(1)(ρ)=1/T(1)(ρ) appears over a range of easily accessible B(1) values. Measurements of T(1)(ρ) at constant temperature and different B(1) values then give the "dispersion profiles" for biopolymers. Fitting a theoretical relaxation model to these profiles allows for the estimation of correlation times. This way of obtaining the correlation time is easier and faster than approaches involving measurements of the temperature dependence of R(1)=1/T(1). The T(1)(ρ) dispersion approach, as a tool for molecular dynamics study, has been demonstrated for several hydrated biopolymer systems including crystalline cellulose, starch of different origins (potato, corn, oat, wheat), paper (modern, old) and lyophilized proteins (albumin, lysozyme).     

Hemolysis of Erythrocytes and Erythrocyte Membrane Fluidity Changes by New Lysosomotropic Compounds

This work contains the results of studies on the influence of newly synthesized lysosomotropic substances (lysosomotropes) on human erythrocytes. Six homologous series of the compounds differing in the alkyl chain length and counterions were studied. They were found to hemolyse erythrocytes and to change their osmotic resistance. The observed hemolytic effects were dependent both on the compounds structure (polar head dimension and alkyl chain length of compound) and its form (the kind of the counterion). In parallel, the influence of lysosomotropes on fluidity of the erythrocyte membrane was studied. Three different fluorescent probes were used; 1,6-diphenyl-1,3,5-hexatriene (DPH), 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene, p-toluenesulfonate (TMA-DPH) and 6-dodecanoyl-2-dimethylaminonaphthalene (laurdan). Their anisotropy (DPH and TMA-DPH) or general polarization (laurdan) values after incorporation into ghost erythrocyte membranes were measured. The results obtained show that fluidity changes accompanied the effects observed in hemolytic experiments both quantitatively and qualitatively.     

High-throughput backbone resonance assignment of small 13C,15N-labeled proteins by a triple-resonance experiment with four sequential connectivity pathways using chemical shift-dependent, apparent 1J(1H,13C): HNCACBcodedHAHB

The proposed three-dimensional triple-resonance experiment HNCACBcodedHAHB correlates sequential 15N, 1H moieties via the chemical shifts of 13Calpha, 13Cbeta, 1Halpha, and 1Hbeta. The four sequential correlation pathways are achieved by the incorporation of the concept of chemical shift-coding [J. Biomol. NMR 25 (2003) 281] to the TROSY-HNCACB experiment. The monitored 1Halpha and 1Hbeta chemical shifts are then coded in the line shape of the cross-peaks of 13Calpha, 13Cbeta along the 13C dimension through an apparent residual scalar coupling, the size of which depends on the attached hydrogen chemical shift. The information of four sequential correlation pathways enables a rapid backbone assignment. The HNCACBcodedHAHB experiment was applied to approximately 85% labeled 13C,15N-labeled amino-terminal fragment of Vaccinia virus DNA topoisomerase I comprising residues 1-77. After one day of measurement on a Bruker Avance 700 MHz spectrometer and 8 h of manual analysis of the spectrum 93% of the backbone assignment was achieved.     

Qualitative properties of modified equations

Suppose that a consistent one-step numerical method of orderr is applied to a smooth system of ordinary differential equations.Given any integer m 1, the method may be shown to be of orderr + m as an approximation to a certain modified equation. Ifthe method and the system have a particular qualitative propertythen it is important to determine whether the modified equationsinherit this property. In this article, a technique is introducedfor proving that the modified equations inherit qualitativeproperties from the method and the underlying system. The techniqueuses a straightforward contradiction argument applicable toarbitrary one-step methods and does not rely on the detailedstructure of associated power series expansions. Hence the conclusionsapply, but are not restricted, to the case of Runge-Kutte methods.The new approach unifies and extends results of this type thathave been derived by other means: results are presented forintegral preservation, reversibility, inheritance of fixed points.Hamiltonian problems and volume preservation. The techniquealso applies when the system has an integral that the methodpreserves not exactly, but to order greater than r. Finally,a negative result is obtained by considering a gradient systemand gradient numerical method possessing a global property thatis not shared by the associated modified equations.     

Toward Exact Analytical Wave Function of Helium Atom: Two Techniques for Constructing Homogeneous Functions of Kinetic Energy Operator

We discuss two general techniques for constructing homogeneous functions c of the kinetic energy operator T for the helium atom in a state of symmetry S. The first technique is based on algebraic identification of the kernel of T in a space spanned by some predetermined set of basis functions. The second technique, analytic in nature, constructs the homogeneous functions of T as formal power series with coefficients deduced from recurrence relations stemming from the requirement Tc=0. Both approaches are capable of producing a great variety of homogeneous functions c with arbitrary homogeneity that can prove useful for constructing the exact ground state wave function for the helium atom.