Modified GOESY in the analysis of disaccharide conformation

One-dimensional nuclear magnetic resonance techniques were applied to the conformational investigation of a disaccharide. More specifically, nuclear Overhauser enhancements (NOEs) of protons on either side of the glycosidic bond have been used to determine the conformation of the disaccharide alpha-l-Rhap-(1 --> 2)-alpha-l-Rhap-OMe. A modified GOESY sequence, incorporating selective excitation and pulsed field gradient enhancement, was developed and used to accurately measure small NOE signals of interest. These experiments were named M-GOESY, for modified GOESY, and the data they provided were used to calculate internuclear distances in the disaccharide molecule. The accuracy of the M-GOESY measurements was enhanced by elimination of indirect effects, or spin diffusion, by selective inversion(s) of either the intermediate magnetization or the source and target magnetization during the mixing time. Results of this study indicate that the alpha-l-Rhap-(1 --> 2)-alpha-l-Rhap-OMe disaccharide molecule exists primarily in one conformation, with the glycosidic torsion angle psi approximately -30 degrees based on past molecular dynamics simulations.     

Theoretical analysis of the influence of flexoelectric effect on the defect site in nematic inversion walls

Based on the experimental phenomena of flexoelectric response at defect sites in nematic inversion walls conducted by Kumar et al., we gave the theoretical analysis using the Frank elastic theory. When a direct-current electric field normal to the plane of the substrate is applied to the parallel aligned nematic liquid crystal cell with weak anchoring, the rotation of ± 1 defects in the narrow inversion walls can be exhibited. The free energy of liquid crystal molecules around the +1 and-1 defect sites in the nematic inversion walls under the electric field was formulated and the electric-field-driven structural changes at the defect site characterized by polar and azimuthal angles of the local director were simulated. The results reveal that the deviation of azimuthal angle induced by flexoelectric effect are consistent with the switching of extinction brushes at the +1 and-1 defects obtained in the experiment conducted by Kumar et al.     

Quantum Associative Memory with Improved Distributed Queries

The paper proposes an improved quantum associative algorithm with distributed query based on model proposed by Ezhov et al. We introduce two modifications of the query that optimized data retrieval of correct multi-patterns simultaneously for any rate of the number of the recognition pattern on the total patterns. Simulation results are given.     

Rotational resonance NMR of 13C2-labelled retinal: quantitative internuclear distance determination.

Rotational resonance phenomena are investigated in the solid-state magic-angle spinning NMR of all-E-[11,20-13C2]-retinal at a magnetic field of 4.7 T. We find good agreement between experiments and numerical simulations for the rotational resonance spectral peakshapes and for the rotor-driven magnetization exchange. The internuclear distance between the 13C-labelled C11 and C20 sites is determined to be 0.301 +/- 0.008 nm (from rotational resonance spectra) and 0.300 +/- 0.010 nm (from rotor-driven magnetization exchange), in agreement with the X-ray crystallographic distance of 0.296 nm. We show rotational resonance spectra which display perturbations from intermolecular homonuclear spin-spin interactions.     

Efficient double-quantum excitation in rotational resonance NMR

We present a new technique for double-quantum excitation in magic-angle-spinning solid-state NMR. The method involves (i) preparation of nonequilibrium longitudinal magnetization; (ii) mechanical excitation of zero-quantum coherence by spinning the sample at rotational resonance, and (iii) phase-coherent conversion of the zero-quantum coherence into double-quantum coherence by frequency-selective spin inversion. The double-quantum coherence is converted into observable magnetization by reversing the excitation process, followed by a pi/2 pulse. The method is technically simple, does not require strong RF fields, and is feasible at high spinning frequencies. In [(13)C(2),(15)N]-glycine, with an internuclear (13)C-(13)C distance of 0.153 nm, we achieve a double-quantum filtering efficiency of approximately 56%. In [11, 20-(13)C(2)]-all-E-retinal, with an internuclear (13)C-(13)C distance of 0.296 nm, we obtain approximately 45% double-quantum filtering efficiency.     

Collision cross sections between some rovibrational states of ammonia gas perturbed by hydrogen

We have studied lines mixing induced by collisions in the ₄ IR band of ammonia colliding by hydrogen. We have observed a narrowing effect in the inversion doublets. The lineshapes were analysed using an adapted form of Broquier et al. (4). Comparison between our measurements and a semiclassical calculations shows a good agreement.     

Acquired polarization ink·I PNC experiments

Parity non-conserving neutron transmission asymmetries have been calculated for unpolarized beams on polarized targets. As the neutron beam propagates through a polarized target, some components are preferentially absorbed. This acquired polarization complicates the interpretation of transmission measurements. We extend the analysis of Postma et al. to include parity mixing in the neutron resonances and emphasize the importance of the nuclear resonance spectroscopy. The relative importance of the acquired polarization contribution is determined by the spectroscopic parameters.     

从单个混合时间的2D NOESY峰强度矩阵求取核间距

提出了从单个混合时间的2D NOESY峰强度或混合系数矩阵直接求取核间距的新方法。该方法分成二步进行。第一步采用规范化2D NOESY峰强度或对称化混合系数矩阵来计算对称化核交叉弛豫速率矩阵。其优点是计算过程简单且普适。第二步直接用对称化核交叉弛豫速率来求取核间距。该过程考虑到分子内部运动的贡献。本文方法是自治的,只要能测出单个混合时间的2D NOESY峰强度或混合系数矩阵即可直接求出自旋系统的核间距了。     

Optimizing tissue contrast in magnetic resonance imaging

Magnetic resonance imaging demands that tissue contrast and signal-to-noise advantages be sought in each component of the imaging system. One component of magnetic resonance imaging in which contrast and signal-to-noise ratios are easily manipulated is in the choice of pulse sequences and interpulse delay times. This article provides a general method for determining the best choices of interpulse delay times in pulse sequences and applies that method to saturation recovery, inversion recovery, and spin-echo sequences. Saturation recovery and inversion recovery sequences with rephasing pulses, and tissues with unequal hydrogen densities are considered. Optimization of pulse sequences is carried out for the two distinct cases of (a) a fixed number of sequence repetitions and (b) a fixed total imaging time. Analytic expressions are derived or approximate expressions are provided for the interpulse delay times that optimize contrast-to-noise ratios in each pulse sequence. The acceptable range of interpulse delay times to obtain reasonable contrast using each pulse sequence is discussed.     

Measurement of the parity-violating asymmetry in inclusive electroproduction of π- near the Δ0 resonance

The parity-violating (PV) asymmetry of inclusive π- production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Δ0 resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Δ)- that characterizes the parity-violating γNΔ coupling. Zhu et al. calculated d(Δ)- in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(γ)-=-5.2 to +5.2 ppm. The measurement performed in this work leads to A(γ)-=-0.36±1.06±0.37±0.03 ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V(ud)/V(us). The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N-Δ axial transition form factors using PV electron scattering.     

Determination of Spatial Distribution of Plasma Electrons by Multibeam FIR Interferometry

The spatial distribution of plasma electrons in the ISX-B Tokamak has been determined by Abel-inverting vertical integral data from far infrared (FIR) laser-phase shift measurements. The calculational method for performing the Abel inversion is discussed and the results of the inversion of several sets of data are compared with Thomson scattering measurements of the pointwise electron density, and with the 2-mm interferometer measurement of the horizontal-midplane line-integral electron density. The inversion method used is essentially that described by Demas et al. This method is an extension of the method described by Yasutomo et al. The main difference is that the inversion method used here can treat plasmas with any outer boundary shape as long as the radius of the surface is single valued. In this regard it is more general than the inversion method of Wetzer, which is restricted to using an elliptical outer-plasma boundary.     

Antiphase dynamics of a multimode quantum well semiconductor laser

A novel multilongitudinal mode model of a semiconductor laser is presented. The model takes into account four-wave mixing of the longitudinal modes and is based on the correct procedure of simultaneous expansion of the population inversion in time and space series. It is shown that the model has antiphase regimes similar to those observed in experiment. Such behavior exists in a narrow range of the carrier diffusion coefficient, which allows us to estimate the value of this parameter.     

Time-of-flight variant to image mixing of granular media in a 3D fluidized bed

This paper describes a variant of time-of-flight magnetic resonance (MR) imaging that provides a method of measuring the inherent mixing in a fluidized bed without the introduction of tracer particles. The modifications to conventional time-of-flight imaging enable the measurement of the axial mixing of a precisely controlled initial particle distribution, thereby providing measurements suitable for a direct comparison with models of solids mixing in granular systems. The imaging sequence is applied to characterize mixing, over time scales of 25-1000 ms, in a gas-fluidized bed of Myosotis seed particles; mixing over short timescales, inaccessible using conventional tracer techniques, is studied using this technique. The mixing pattern determined by this pulse sequence is used in conjunction with MR velocity images of the motion of the particles to provide new insight into the mechanism of solids mixing in granular systems.     

Nuclear time delay in resonant heavy ion collisions

From a quantum mechanical model for quasielastic nuclear scattering, involving a pocket in the internuclear potential, we derive a distribution of nuclear delay times. We show that coherent excitation of states in a rotational band of nuclear resonances leads to a lighthouse effect in the nuclear scattering cross section. Its influence on atomic excitations is shortly discussed for the case of positron creation in supercritical heavy ion collisions.     

EPR study of the hemoglobin rotational correlation time and microviscosity during the polymerization of hemoglobin S

The microviscosity and the protein rotational correlation time are analyzed in samples of hemoglobin A and hemoglobin S with the intracellular concentration at 36°C and during spontaneous deoxygenation. With this purpose, we use glutathione and carbonmonoxy hemoglobin labeled with 4-maleimido-2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) as probes and 4-maleimido TEMPO bound to the hemoglobin (A and S) as a spin label. The saturation transfer electron paramagnetic resonance experiment showed a sigmoidal behavior, and an increase (about twice) of the hemoglobin rotational correlation time and microviscosity during the polymerization process of hemoglobin S. The delay time determined by this method coincides with that obtained in proton magnetic resonance experiments. These results help to explain the temporal behavior of the proton relaxation times obtained in samples of hemoglobin A and S under the same experimental conditions.     

NOESY around the critical point ωτc = 1.12. Precise determination of proton-proton distances and reorientation correlation times with two-field NOESY

When nuclear Overhauser enhancement spectroscopy (NOESY) experiments are performed around the critical point ωτ_c = 1.12, internuclear cross-relaxation rates are dependent on the resonance frequency ω, where τ_c is the reorientation time of the distance vector between two magnetic dipoles. Therefore, the correlation times and, consequently, the internuclear distances can be determined precisely by measuring the cross-relaxation rates under two magnetic fields. An application with a cyclic pentapeptide is given as an example, demonstrating the use of the two-field NOESY method in molecular structure studies. NOESY experiments with mixing times beyond 500 ms are discussed.     

On the use of tryptophan to detect slow orientational motions

For our investigations on orientational motions of membrane proteins with the method of time-resolved fluorescence anisotropy decay (TRFA), we first wanted to test the use of tryptophan fluorescence in detecting slow motions on the time scale of tens of nanoseconds and to get more insight into the possible motions of membrane proteins by investigating a simple system. We performed TRFA measurements on a short α-helical 21-amino acid peptide in different environments (Vogel, H.,et al. Proc. Natl. Acad. Sci. USA 85, 5067–5071, 1988). In each case, we got three relexation time constants. The longest of these depends strongly on changes in the environment, whereas the two shorter times show only weak dependencies. So we conclude that the longest time belongs to the rotational diffusion of the entire peptide and the other to internal motions.     

Rotationally mediated selective adsorption in rigid rotor/rigid surface scattering

We present a detailed investigation of a new effect in molecule/surface scattering, rotationally mediated selective adsorption, which has been first observed by Cowin et al. (J. Chem. Phys. 75 (1981) 1033) in rotationally inelastic HD/Pt (111) scattering. It is due to resonance between an asymptotically closed rotational channel and a vibrational bound state of the molecule/surface system. Exact close-coupling and diffractionally sudden calculations are performed for HD scattered from a rigid, flat and weakly corrugated surface. Both variation of the collision energy and variation of the incident angle are considered. In the latter case we include the averaging over the collision energy of the initial beam and compare qualitatively our results with the experiment. Taking into account the resonances below they j = 0 → 1 threshold we are able to explain all of the experimentally observed resonances and to assign them with the appropriate rotational-vibrational quantum numbers. The largest deviation between experimental and theoretical resonance angles is ~ 1.6° at a collision energy of E = 109 meV. An interesting interference effect is found in the case of weak surface corrugation. Although the diffractionally sudden approximation generally gives only poor results, it also reproduces this effect and provides a simple explanation of it in terms of the Breit-Wigner representation of the S-matrix.     

Asymmetric delay feedback stochastic resonance detection method based on prior knowledge particle swarm optimization

For the adjustable parameters stochastic resonance system, the selection of the structural parameters plays a decisive role in the performance of the detection method. The vibration signal of rotating machinery is non-linear and unstable, and its weak fault characteristics are easily concealed by noise. Under strong background noise interference, the detection of fault features is particularly challenging. Therefore, a type of weak fault feature extraction method, named knowledge-based particle swarm optimization algorithm for asymptotic delayed feedback stochastic resonance (abbreviated as KPSO-ADFSR) is proposed. Through deduction under adiabatic approximation, we observe that both the asymmetric parameters, the length of delay and the feedback strength, impact the potential function. After adjusting the asymmetric parameters of the system, the output signal-to-noise ratio (SNR) is used as the fitness function, and the setting of the relationship between the noise intensity and barrier height is used as the prior knowledge of the particle swarm algorithm. Through this algorithm, the delay length and the feedback strength are optimized. This method achieves global optimization of system parameters in a short time; it overcomes the shortcomings of the traditional stochastic resonance method, which has a long convergence time and tends to easily fall into local optimization. It can effectively improve the detection of weak fault features. In the bearing rolling body pitting corrosion failure experiment and steel field engineering experiment, the proposed method could extract the characteristics of a weak fault more effectively than the traditional stochastic resonance method based on the standard particle swarm algorithm.     

Fast calculation technique for scattering in T-matrix method

In scattering calculations using the T-matrix method, the calculation of the T-matrix involves multiplication and inversion of matrices. These two types of matrix operations are time-consuming, especially for the matrices with large size. Petrov et al. [D. Petrov, Y. Shkuratov, G. Videen, Opt. Lett. 32 (2007) 1168] proposed an optimized matrix inversion technique, which suggests the inversion of two matrices, each of which contains half the number of rows. This technique reduces time-consumption significantly. On the basis of this approach, we propose another fast calculation technique for scattering in the T-matrix method, which obtains the scattered fields through carrying out only the operations between matrices and the incident field coefficient. Numerical results show that this technique can decrease time-consumption by more than half that of the optimized matrix inversion technique by Petrov et al.