Correlation of transverse and rotational diffusion coefficient: A probe of chemical composition in hydrocarbon oils

Measurements of relaxation time and diffusion coefficient by nuclear magnetic resonance are well-established techniques to study molecular motions in fluids. Diffusion measurements sense the translational diffusion coefficients of the molecules, whereas relaxation times measured at low magnetic fields probe predominantly the rotational diffusion of the molecules. Many complex fluids are composed of a mixture of molecules with a wide distribution of sizes and chemical properties. This results in correspondingly wide distributions of measured diffusion coefficients and relaxation times. To first order, these distributions are determined by the distribution of molecular sizes. Here we show that additional information can be obtained on the chemical composition by measuring two-dimensional diffusion-relaxation distribution functions, a quantity that depends also on the shape and chemical interactions of molecules. We illustrate this with experimental results of diffusion-relaxation distribution functions on a series of hydrocarbon mixtures. For oils without significant amounts of asphaltenes, the diffusion-relaxation distribution functions follow a power-law behavior with an exponent that depends on the relative abundance of saturates and aromatics. Oils with asphaltene deviate from this trend, as asphaltene molecules act as relaxation contrast agent for other molecules without affecting their diffusion coefficient significantly. In waxy oils below the wax appearance temperature a gel forms. This is reflected in the measured diffusion-relaxation distribution functions, where the restrictions due to the gel network reduce the diffusion coefficients without affecting the relaxation rates significantly. © 2008 American Chemical Society

Rodlike polymer gelatination as studied by PFG NMR: Fibrin polymerization in human plasma

The structure formation in rodlike polymers was investigated by the example of polymerization of fibrin rodlike molecules in native plasma. Translational mobility of fibrin molecules in anticoagulated plasma and native plasma during fibrin polymerization was studied by pulse field gradient nuclear magnetic resonance. It was shown that the diffusion decay of anticoagulated plasma can be fitted by the sum of exponents and fibrin molecules have the self-diffusion coefficient Df of 1.53·10-11 m2/s. The diffusion decay of native plasma during fibrin polymerization becomes nonexponential and is described by the lognormal distribution of fibrin self-diffusion coefficients. Qualitative and quantitative changes of the spectrum of fibrin self-diffusion coefficients (SDCs) during polymerization were investigated and analyzed. A symmetrical broadening of the spectrum at the beginning of polymerization and symmetrical narrowing at its final stages with conservation of the most probable SDC was explained on the basis of the hypothesis about the simultaneous action of fibrin polymerization and lyses

Porous media characterization by PFG and IMFG NMR

Fully and partially filled with tridecane quartz sand was studied by different NMR techniques. The set of NMR experiments was carried out to obtain information about porous media geometry and fluid localization in it in case of partially filled porous space. The study was done using three NMR approaches: pulse field gradient NMR (PFG NMR), DDif experiment and tau-scanning experiment. The possibility to use all three approaches to study porous media properties even at the high resonance frequency is shown together with complementarity of the given by them information. Thus, first two approaches give information about porous sizes and geometry, at the same time tau-scanning experiment allows us to obtain information about distribution of internal magnetic field gradients in the porous space and draw conclusions about fluid localization in it. © 2007 Elsevier Inc. All rights reserved

Effect of oxygen on the NMR relaxation properties of crude oils

Nuclear magnetic resonance relaxation measurements of bulk fluids provide a sensitive probe of the dynamics of molecular motion. Dissolved oxygen can interfere with this technique as its paramagnetic nature leads to a reduction of the paramagnetic relaxation times of the fluids. We studied this effect for the relaxation properties of crude oils that are in general characterized by a distribution of relaxation times. The samples were stock tank oils that have been exposed to air. We compared T1 and T2 relaxation time distributions and their correlation functions of the initial (oxygenated) samples with those from the deoxygenated samples. Oxygen was removed from the oils with a freeze-thaw technique. As expected, the effect of oxygen is most apparent in oils with long relaxation times. In these oils the effect of oxygen can be described by an additional relaxation rate 1/T1,2 ox to the transverse and longitudinal relaxation rates that is sample dependent but does not vary within the relaxation time distribution of the oil. Values of 1/T1,2 ox for different crude oils were found to be in the range of 2.5 to 8.3 s. For crude oils that have components with relaxation times less than 100 ms, no significant oxygen effect is observed. © Springer-Verlag 2005

Considerations and strategies for incorporating lived experience in mental health research

Introduction: Incorporating lived experience in mental health research deserves special focus due to the unique stigma faced by those with lived experience and the unique gap between the experience and expression of mental health struggle.https://knowledgeconnection.mainehealth.org/lambrew-retreat-2023/1029/thumbnail.jp

Pathways to Care of Maine Youth with Psychosis

Study clinicians conducted semi-structured interviews to identify the timing and steps of each person’s Pathway to Care (PtC).https://knowledgeconnection.mainehealth.org/lambrew-retreat-2023/1028/thumbnail.jp

Effects of drugs on water permeability of erythrocyte membranes

The method of NMR-relaxation with the manganese doping has been applied to study changes of water permeability of red blood cell membranes affected by various concentrations of chlorhexidine digluconate and dimephosphone. It is shown that both investigated substances suppress the water permeability of the red blood cell membrane in a dose-dependent manner. Half-maximum inhibitory effect of studied substances was reached at the concentrations of 9 μM of chlorhexidine and 400 μM of dimephosphone. © 2010 Pleiades Publishing, Ltd

Effects of drugs on the permeability of erythrocyte membranes for water

The method of a NMR-relaxation with a paramagnetic doping has been applied to study changes of water permeability of red blood cell membranes under the action of chlorhexidine digluconate and dimephosphone. It is shown that both investigated substances suppress the water permeability of the red blood cell membrane in a dose-dependent manner. Chlorhexidine exerted a half-maximum effect at the concentration of 9 μM and dimephosphone, at 400 μM

Off-Pump Surgical Treatment of Anomalous Origin of the Left coronary Artery from the Pulmonary Artery

An anomalous origin of the left coronary artery from the pulmonary artery, or Blund – White – Garland syndrome, is a rare congenital heart disease in which an anatomically correctly formed left coronary artery extends away from the pulmonary artery. Most patients with this defect die from progressive left ventricular failure during the first year of life, and the rest may suddenly die in adolescence or adulthood from acute coronary insufficiency. Several surgical methods of correction of the defect have been proposed, but a small number of observations do not allow one to express unequivocally in favor of one of the methods of performing the operation. We present our own observation of a surgical correction of a defect in a teenager. We performed off-pump aortocoronary bypass surgery of the anterior interventricular artery, and separation of the left coronary artery from the pulmonary artery by ligation, with the stitching of the left coronary artery. The issue of the expediency of tying hypertrophied collaterals between right coronary artery and left coronary artery systems was discussed with the purpose of reducing competitive blood flow after performing left coronary artery shunting. Experience in performing coronary artery bypass surgery without artificial circulation made it possible to perform an off-pump operation

Porous media characterization by PFG and IMFG NMR

Fully and partially filled with tridecane quartz sand was studied by different NMR techniques. The set of NMR experiments was carried out to obtain information about porous media geometry and fluid localization in it in case of partially filled porous space. The study was done using three NMR approaches: pulse field gradient NMR (PFG NMR), DDif experiment and tau-scanning experiment. The possibility to use all three approaches to study porous media properties even at the high resonance frequency is shown together with complementarity of the given by them information. Thus, first two approaches give information about porous sizes and geometry, at the same time tau-scanning experiment allows us to obtain information about distribution of internal magnetic field gradients in the porous space and draw conclusions about fluid localization in it. © 2007 Elsevier Inc. All rights reserved