Magnetic Resonance Relaxation Time Measurements Research Articles

Multi-shelled hollow porous carbon nanospheres-based evaporator for highly efficient solar-driven desalination

Carbon-based materials stand out as photothermal materials for interfacial solar evaporation due to their high solar absorptance, chemical stability, adjustable structure, ease of preparation, and low cost compared to other candidate materials. Development of multifunctional carbon-based materials that can endow the fabricated evaporators with reduced energy loss and evaporation enthalpy is highly demanded to achieve extraordinary evaporation rates. Herein, high-solar-absorptivity multi-shelled hollow porous carbon nanospheres are fabricated and incorporated with an insulating hydrogel bottom layer into an integrated solar evaporator. It achieves a fast photothermal response and a remarkably high solar evaporation rate of 2.4 kg m−2 h−1 under one sun. Multiphysics simulation indicates that the porous multi-shelled hollow structure enables sufficient and effective interactions between water and the hydrophilic carbon surfaces, thus producing more intermediate water (IW) and lowering the evaporation enthalpy. The solar-driven water evaporation in the evaporator is probed by in-situ low-field nuclear magnetic resonance relaxation time measurements, based on which conversion of free water (FW) into IW during solar evaporation is proposed. The molecular dynamics simulations reveal that the evolution of FW clusters into IW is facilitated on the carbon surface, thus replenishing the evaporated IW and maintaining continuous high evaporation rates. The demonstrated solar evaporator exemplifies the effectiveness of structural and thermal management in enhancing solar-driven desalination.

Physicochemical and Morphological Study of the Saccharomyces cerevisiae Cell-Based Microcapsules with Novel Cold-Pressed Oil Blends

Vegetable oils rich in polyunsaturated fatty acids are a valuable component of the human diet. Properly composed oil blends are characterized by a 5:1 ratio of ω6/ω3 fatty acids, which is favorable from a nutritional point of view. Unfortunately, their composition makes them difficult to use in food production, as they are susceptible to oxidation and are often characterized by a strong smell. Encapsulation in yeast cells is a possible solution to these problems. This paper is a report on the use of native and autolyzed yeast in the encapsulation of oils. The fatty acid profile, encapsulation efficiency, morphology of the capsules obtained, and thermal behavior were assessed. Fourier transform infrared analysis and low-field nuclear magnetic resonance relaxation time measurements were also performed. The process of yeast autolysis changed the structure of the yeast cell membranes and improved the loading capacity. Lower encapsulation yield was recorded for capsules made from native yeast; the autolysis process significantly increased the value of this parameter. It was observed that NY-based YBMCs are characterized by a high degree of aggregation, which may adversely affect their stability. The average size of the AY capsules for each of the three oil blends was two times smaller than the NY-based capsules. The encapsulation of oils in yeast cells, especially those subjected to the autolysis process, ensured better oxidative stability, as determined by DSC, compared to fresh blends of vegetable oils. From LF NMR analysis of the relaxation times, it was shown that the encapsulation process affects both spin-lattice T1 and spin-spin T2* relaxation times. The T1 time values of the YBMCs decreased relative to the yeast empty cells, and the T2* time was significantly extended. On the basis of the obtained results, it has been proven that highly unsaturated oils can be used as an ingredient in the preparation of functional food via protection through yeast cell encapsulation.

Advances in Electronics Prompt a Fresh Look at Continuous Wave (CW) Nuclear Magnetic Resonance (NMR)

Continuous Wave Nuclear Magnetic Resonance (CW-NMR) was a popular method for sample interrogation at the birth of magnetic resonance but has since been overlooked by most in favor of the now more popular pulsed techniques. CW-NMR requires relatively simple electronics although, for most designs, the execution is critical to the successful implementation and sensitivity of the system. For decades there have been reports in the literature from academic groups showing the potential of magnetic resonance relaxation time measurements in industrial applications such as the production of food and drink. However, the cost, complexity and power consumption of pulsed techniques have largely consigned these to the literature. Advances in electronics and developments in permanent magnet technology now require a fresh look at CW-NMR to see if it is capable of providing cost effective industrial solutions. In this article, we review the electronics that are needed to undertake a continuous wave NMR experiment starting with early designs and journeying through the literature to understand the basic designs and limitations. We then review the more recent developments in this area and present an outlook for future work in the hope that more of the scientific community will take a fresh look at CW-NMR as a viable and powerful low-cost measurement technique.

Solid-State Nuclear Magnetic Resonance Study of the Physical Stability of Electrospun Drug and Polymer Solid Solutions

A major challenge in utilizing the amorphous form of an active pharmaceutical ingredient (API) in a final oral dosage form is preventing crystallization over time and ensuring stability. One method to improve stability is lowering the mobility of an API by formulating as a solid solution with an excipient. In this work, we use electrospinning to prepare solid solutions of API, aliskiren (SPP) or indomethacin (IND), and a polymer, polyvinylpyrrolidone (PVP). The stability of the solid solutions over 6-month storage in a desiccator at 40 °C was investigated. Using X-ray diffraction and differential scanning calorimetry, it was determined that no crystals were present in the four formulations tested--1:1 SPP-PVP, 4:1 SPP-PVP, 1:1 IND-PVP, and 2:1 IND-PVP at any time. Solid-state nuclear magnetic resonance relaxation time measurements were used to determine whether phase separation of the API and polymer occurred during the study period. It was found that all formulations remained homogeneous down to at least a 2-10 nm length scale, indicating that for these APIs, electrospinning is an acceptable method for forming stable amorphous solid solutions.

MAGNETIC RESONANCE RELAXATION-TIME STUDIES OF FRACTURE REPAIR IN CHICKS: A POTENTIAL METHOD FOR EVALUATION OF FRACTURE HEALING

Purpose: To investigate whether magnetic resonance relaxation-time measurements have a role in monitoring fracture healing. Methods: Magnetic resonance relaxation-time measurements were used to assess callus formation in chicks' tibiae and were correlated to the histopathologic and biomechanical changes that occur throughout the process of fracture repair. Results: The effective transverse relaxation time (T2) values recorded during fracture healing process were significantly longer (p = 0.0151) at day 14 (65.5575 ms.), compared with those recorded at days 3 (52.68 ms.) and 7 (55.4313 ms.). The T2 values distributions (a) at day 14 (0.2304) were significantly lower (p = 0.0313) compared with those recorded at days 7 (0.2721) and 10 (0.2742). Using a semiquantitative histologic evaluation, a significant increase in the amount of endosteal new bone (p = 0.048), and periosteal new bone (p = 0.008), associated with a significant decrease in the amount of old bone (p = 0.007) and cartilaginous tissue (p = 0.001) was observed. Analysis of the torque-angle curves demonstrated a low torque and a large angular deformation associated with low stiffness at 3–7 days post-fracture, and a high torque and a small angular deformation associated with high stiffness at 10–14 days post-fracture. Interpretation: Magnetic resonance relaxation-time follows the histopathologic and biomechanical changes occurring during the process of fracture repair and it may have a role as a potential method for objective estimation of fracture repair.

Earliest cardiac toxicity induced by iron overload selectively inhibits electrical conduction.

Female guinea pigs were injected intraperitoneally with 0.083 g/kg iron dextran (Fe-D) to achieve progressively increasing levels of iron load; controls received dextran. Delayed and blocked cardiac conductivity at the Purkinje fiber-papillary muscle junction was initially observed with Fe-D loads of 0.33 g/kg. Serial magnetic resonance relaxation time measurements obtained from livers of live animals showed a decrease (8.1 +/- 0.86 vs. 14.8 +/- 1.03 ms in controls, P < 0.001) that was first observed in animals loaded with 0.25 g/kg Fe-D. Iron concentrations in hearts and livers were significantly increased (P < 0.001). Left ventricular pressure measurements on 1.5 g/kg Fe-D animals failed to demonstrate a defect in contractility, but 27% (9/33) (P < 0.050) of the animals died without warning signs. We conclude that 1) initial decreases in liver magnetic resonance-relaxation time occur in the same range of iron excess as the threshold of iron load that induces delay or blockade of cardiac conduction and 2) a high incidence of sudden death, presumably from cardiac arrhythmias, was observed with large doses of iron that did not decrease left ventricular contractility.

Developmental changes in proton magnetic resonance relaxation times of cardiac and skeletal muscle.

Proton magnetic resonance relaxation time measurements were used to study developmental changes in rabbit cardiac and skeletal muscles during the last days of gestation and at several postnatal times. Tissue water content decreased steadily during late fetal and early postnatal stages of development. During this period T1 and T2 for cardiac and skeletal muscles also decreased. The relaxation times stabilized after the 20th postnatal day, and at this juncture the T1 and T2 values for myocardium remained consistently higher than for skeletal muscle. The developmental changes in proton relaxation time probably represent changes in water distribution and mobility as well as macromolecular structure during muscle maturation.

The rate of thermally activated methyl group rotation in solids

Evidence is presented which suggests that the thermally activated reorientation rate tau -1 of methyl groups in a very wide range of solids closely follows a universal law which relates tau -1 to the hindering barrier height V and the temperature theta . Thus tau -1 simply measures theta with a calibration curve dependent on V. A simple theory of the calibration curves is described, using a thermal average over all methyl group torsion-rotation states of the modulus of the expectation value of angular momentum. No adjustable parameters are involved if a simple cosine hindering potential is assumed. The relationship is tested on a large number of methyl-containing solids for which V has been deduced from measurements of the tunnel splitting at low temperatures. The predicted temperature-dependent reorientation rate turns out to be very similar to that given by a modified version of the theory of Stejskal and Gutowsky (1958). The relationship between the theories is discussed. Comparison is made with experimental data derived from magnetic resonance relaxation time measurements, and from inelastic neutron scattering studies.

P.M.R. relaxation time studies in some binary liquid systems

Proton magnetic resonance relaxation time measurements have been carried out in mixtures of water with formic acid, acetic acid, propionic acid and n-butyric acid. On account of molecular association, the results reveal strong deviation of these mixtures from the ideal behaviour. The molecular association effect is discussed in some detail. The molecular association ratios determined from the present studies are in excellent agreement with those obtained by the ultrasonic absorption technique. It is further shown that N.M.R. relaxation time studies reveal more information about molecular interactions in liquids than the ultrasonic absorption studies.

Nuclear magnetic resonance relaxation study of water absorbed on milled northern white-cedar

1H nuclear magnetic resonance relaxation time measurements are reported for water equilibrated on milled Northern white-cedar wood. At water contents below 0.38 g of water per gram of dry wood, no freezing event is detected in the NMR experiment. At water contents greater than this transverse relaxation is nonexponential, but may be understood using a simple model. Longitudinal relaxation is nonexponential throughout the water content range studied; however, the data may not be analyzed using the concept of preferential filling of successive layers of water. The magnitudes of the relaxation times measured require that the motion of the average water molecule adsorbed to the wood surface be very rapid with correlation times for reorientation of the interproton vector on the order of nanoseconds at 240°K.

Blood Flow Rates by Nuclear Magnetic Resonance Measurements

Blood flow rates may be determined by nuclear magnetic resonance relaxation time measurements. A set of experiments carried out on the flow of blood in mice tails has demonstrated the feasibility of the scheme. Two simple measurement methods are described, and the pertinent equations are given. In addition, some procedures for using nuclear magnetic resonance and electron paramagnetic resonance for tracing the flow of specific materials in the body are outlined.