Using Earth’s Field NMR to Study Brine Content in Antarctic Sea Ice: Comparison with Salinity and Temperature Estimates

We report on the use in Antarctica of a portable nuclear magnetic resonance spectrometer which utilizes the Earth’s magnetic field. We obtain estimates of brine content, in samples of sea ice extracted at different depths from the annual ice of McMurdo Sound, in the vicinity of Cape Evans, Ross Island. These measurements are correlated with estimates of brine content obtained from temperature and salinity measurements at each depth, using a knowledge of the phase diagram.     

Exponential almost Runge-Kutta methods for semilinear problems

We present a new class of one-step, multi-value Exponential Integrator (EI) methods referred to as Exponential Almost Runge-Kutta (EARK) methods which involve the derivatives of a nonlinear function of the solution. In order to approximate such derivatives to a sufficient accuracy, the EARK methods will be implemented within the broader framework of Exponential Almost General Linear Methods (EAGLMs) to accommodate past values of this nonlinear function and becoming multistep in nature as a consequence. Established EI methods, such as Exponential Time Differencing (ETD) methods, Exponential Runge-Kutta (ERK) methods and Exponential General Linear Methods (EGLMs) become special cases of EAGLMs. We present order conditions which facilitate the construction of two- and three-stage EARK methods and, when cast in an EAGLM format, we perform a stability analysis to enable a comparison with existing EI methods. We conclude with some numerical experiments which confirm the convergence order and also demonstrate the computational efficiency of these new methods.     

Tracking pore to pore exchange using relaxation exchange spectroscopy

We observe the movement of water over time between pores of differing sizes in Castlegate sandstone. To achieve this, we perform an NMR transverse relaxation exchange experiment for several mixing times. The resulting data are converted to 2D T2 distributions using a 2D inverse Laplace transform (ILT). We show for the first time that quantitative analysis of ILT distributions enables one to extract characteristic times for different pores sizes. This information is potentially useful for permeability determination as well as better understanding of exchange between specific pore subpopulations.     

Using Solvent Diffusion as a Probe To Characterize Lamellar Systems

We present an attempt to characterize planar surfactant aggregates from the measurement of the diffusion of solvent molecules located between the lamellae. Besides anisotropy, those experiments reveal properties of the bilayers such as their orientation, dimension and also the characteristics of their hydrodynamic modes. Experimental results are presented for two different surfactant systems. Significant differences are apparent. Authors' address: Paul T. Callaghan, MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand     

1H NMR spectroscopy of polymers under shear and extensional flow

We discuss the potential insights gained from ¹H nuclear magnetic resonance (NMR) spectroscopy experiments on polymeric systems under both shear and extension, and we show in particular that ¹H spin-spin relaxation is sensitive to both molecular conformation and to molecular interactions. Rheo-NMR ¹H spectroscopy studies on semi-dilute solutions of polyacrylamide demonstrate that the chain protons exhibit a marked T ₂ reduction under shear and that the recovery on shear cessation is indicative of slow reorganisational dynamics. Studies of the wheat flour protein, gluten, indicate marked spectroscopic changes in the vicinity of the amidic resonances associated with glutamine residues, an effect we attribute to the disruption of hydrogen bonding. Received: 23 June 1999/Accepted: 23 August 1999     

Multiple echoes, multiple quantum coherence, and the dipolar field: demonstrating the significance of higher order terms in the equilibrium density matrix.

It is well known that dipolar field effects lead to multiple spin echoes in a simple two-RF pulse experiment (the MSE experiment). We show here that coherence transfer echoes (which identify the existence of multiple quantum coherences in liquid NMR) and multiple spin echoes have a common origin. Using density matrix theory we have calculated the phase and timing of multiple spin echoes from all quadrature phase combinations of RF pulses. We show for the MSE experiment that there is a one-to-one correspondence between the time domain echo order and the multiple quantum coherence order. The experimental confirmation of these phase predictions shows that multiple spin echoes provide independent evidence for the breakdown of the high temperature approximation as proposed by Warren et al. (Science 262, 2005 (1993)).     

用于 EAST 上低杂波平行波数测量的磁探针设计与测试

针对EAST上2.45GHz低杂波,完成了低杂波平行波数测量磁探针的设计、仿真与测试。利用有限元仿真软件COMSOL Multiphysics 5.2对磁探针尺寸进行仿真优化,确定了单匝环、矩形缝以及陶瓷片厚度等影响磁探针耦合性能的关键尺寸。测试结果表明,该磁探针对2.45GHz低杂波有良好的耦合性能和鉴别波极化的能力,与仿真结果一致。研究结果为EAST装置上低杂波平行波数测量诊断系统的建立提供重要的参考依据,从而为进一步开展高密度低杂波电流驱动实验研究提供必要的实验数据。     

Estimation of interaction energies by the critical molecular weight method: 1. Blends with polycarbonates

The interaction energies between PS, Pα-MS, and PMMA with several bisphenol-A-based polycarbonates were quantitatively determined from oligomer/oligomer, oligomer/homopolymer, and homopolymer/copolymer blends. Interaction energies were calculated from the Flory-Huggins theory and the Sanchez-Lacombe equation of state theory using experimental cloud points or miscibility boundaries. Alkyl addition to the phenyl rings of polycarbonate is favorable for miscibility with polystyrene whereas halogenation of the bisphenol connector unit is favorable for miscibility with poly(methyl methacrylate). Interaction energies are quantitatively ranked and described qualitatively in terms of changes in the electronic charge distribution of the polymer repeat units as calculated by SYBYL software. © 1994 John Wiley & Sons, Inc.     

Diffusion-relaxation correlation in simple pore structures

The effects of independent encoding for relaxation and for diffusion using separate time and gradient dimensions are calculated for spins diffusing in plane parallel and spherical pores with relaxing walls. Two-dimensional inverse Laplace transformation is used to obtain computed (D,T(2)) maps for both geometries, in the regime in which the dimensionless diffusion coefficient is less than unity and the dimensionless relaxation parameter of order unity or greater. It is shown that there exist two distinct branches on the (D,T(2)) maps, one with diffusion and relaxation strongly correlated and one in which the diffusion coefficients vary widely independently of relaxation.