Nuclear magnetic cooling

Transitions. Samples containing 50 mol % tetrafluoroethylene with ca 92% alternation were quenched in ice water or cooled slowly from the melt to minimise or maximize crystallinity, respectively (19). Internal motions were studied by dynamic mechanical and dielectric measurements, and by nuclear magnetic resonance. The dynamic mechanical behavior showed that the CC relaxation occurs at 110°C in the quenched sample in the slowly cooled sample it is shifted to 135°C. The P relaxation appears near —25°C. The y relaxation at — 120°C in the quenched sample is reduced in peak height in the slowly cooled sample and shifted to a slightly higher temperature. The CC and y relaxations reflect motions in the amorphous regions, whereas the P relaxation occurs in the crystalline regions. The y relaxation at — 120°C in dynamic mechanical measurements at 1 H2 appears at —35°C in dielectric measurements at 10 H2. The temperature of the CC relaxation varies from 145°C at 100 H2 to 170°C at 10 H2. In the mechanical measurement, it is 110°C. There is no evidence for relaxation in the dielectric data. 

A mixture of 24 g of 1,3-dimethyladamantane and BO ml of bromine was refluxed for 6 hours. The reaction product mixture was cooled, taken up in about 200 ml of chloroform, and poured onto ice. The excess bromine was removed by adding sodium hydrosulfite. The chloroform layer was separated from the aqueous layer, dried, concentrated in vacuo, and distilled at reduced pressure to yield 30.5 g of product having a boiling point of about 11B°C at 5-6 mm np = 1.5169-1.51B2. The product was identified by nuclear magnetic resonance (NMR) and elemental analyses as 1-bromo-3,5-dimethyladamantane. 

Flexible superconducting tapes provide promise of uses for superconductors in motors, generators, and even electric transmission lines. Meanwhile, superconducting magnets cooled to the temperature of liquid helium already are in use. High-field nuclear magnetic resonance (NMR) spectrometers have become standard instruments in chemical research laboratories, and the same type of machine (called an MRI spectrometer) is used for medical diagnosis in hospitals worldwide. 

Since the product slowly darkens on exposure to air, it should be stored under nitrogen in a refrigerator. The compound solidifies on cooling m.p. 16.0-16.5°. Nuclear magnetic resonance spectrum (neat, tetramethylsilane internal standard) singlets at d 7.00 (aromatic protons), 3.93 (CH2), and 2.24 p.p.m. (NH). 

Collected Phase Information for Cerium-Cadmium Alloys. A partial phase diagram for the cerium-cadmium system is presented in Figure 1. The room temperature results are based on x-ray studies by Iandelli and Ferro (9), who studied slowly cooled samples. However, their CeCd6 is shown as a dashed line because nuclear magnetic resonance studies by Jackson and the authors (10) have shown that the compound is unstable at room temperature and can decompose to metallic cadmium and CeCd 4i5. Because of probable kinetic barriers, the absence of compounds intermediate between cadmium and CeCd 6 does not indicate that these intermediates are unstable at room temperature. 

J. A. Jackson, also of this laboratory, has made room temperature nuclear magnetic resonance studies of the Knight shift of cadmium in slowly cooled CeCd, 45 alloys with different compositions and different histories. All CeCd 4 5 samples tested showed a major peak at almost the same position and shifted from that of metallic cadmium. One sample showed only this peak, while others clearly showed satellite peaks either at larger or at smaller shift. Possibly some samples had small amounts of both satellite peaks, and there was apparently some further difference in the shapes of satellite peaks and of the major peak these latter observations are tenuous, however, since they were near the resolution limit of the apparatus. The differences apparently do not correlate simply with composition however, they may correlate with differences in microphase structures. 

The experimental apparatus, as shown in Figure 11-1, was a standard molecular beam machine with a heated pulsed valve for vaporization of the non-volatile species and for supersonic cooling. Samples of 1-methyluracil, 1,3-dimethyluracil and thymine were purchased from Aldrich Co. and used without further purification. The sample 1,3-dimethylthymine was synthesized from thymine following a literature procedure [33], and its purity was checked by nuclear magnetic resonance (NMR) and infrared absorption (IR) spectroscopy. The heating temperatures varied for different samples 130°C for DMU, 150°C for MU, 180°C for DMT, and 220°C for thymine. No indication of thermal decomposition was observed at these... 

If the fat is cooled to some point below the melting point of the highest melting component and allowed to fully equilibrate (crystalhze to the maximum extent in the most stable polymorph), there will be some ratio of sohd to liquid fat dependent on the nature of the TAG mixture in the natural fat. This solid fat content (SFC) is often measured by a pulsed nuclear magnetic resonance (NMR) technique. A plot of the maximum amount of fat crystallized (SFC) at sequentially higher temperatures... 

Fig. 2. Cooling curves for samples in pulsed nuclear magnetic resonance (pNMR), tur-bidimetric, light-scattering, and image analysis experiments.

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