Magnetic temperature

Other university experiments have found that under certain scaling conditions, with the right combination of magnetism, temperature, acidity, and water flow rate, the rate of scaling can be halved and that the scale so formed is not in the form of adherent crystalline deposits, but rather a sludge or powder that is fairly easily removed. 

Fig. 18 Field cooled (FCM), zero field cooled (ZFCM) and remnant (REM) magnetization temperature dependencies of [Mn(Cp )2][Ni(dsit)2]. From [53]...

Suppose the openloop process transfer function relating controlled variable magnet temperature and manipulated variable compressor speed is... 

TD-NMR and HR-NMR spectrometer systems have a majority of components in common. All spectrometers consist of a magnet, magnet temperature sensors, magnet heater power supply, RF frequency synthesizer, pulse programmer, transmitter/amplifier, sample probe, duplexor, preamplifier, receiver, and ADC, all controlled by a computer. In addition to these items a HR-NMR has several other requirements which include an electromagnetic shim set, a shim power supply, and a second RF locking channel tuned to the resonance frequency of Li. The second RF channel is identical to that of the observed H channel. Figures 10.9 and 10.10 show the basic setup of TD-NMR and HR-NMR spectrometers, respectively. 

We have mentioned earlier that, as shown in Fig. 15a, small but perceptible magnetic field variations occur when the magnet temperature changes. 

The magnet temperature variation AT is approximately proportional to the power dissipated by the magnet and therefore to the square of the magnet current I. The variation of AS is a function of AT which reflects the changes in magnet geometry due to thermal dilatations. The net result is... 

Fig. 15. Data acquired in a multi-block NP experiment (32 T-values). (a) Experiment done with the thermal compensation turned Off. The FID offset is clearly not the same for all blocks, revealing magnetic field displacements due to magnet temperature fluctuations. The magnet temperature varies because the power dissipated on it in each block depends on the varying t value, (b) The same experiment with the thermal compensation turned On.

The problem can be partially mitigated by hardware compensation devices (see Section IV.D). A complementary approach consists in setting up preparatory sequences which balance the average per-block thermal dissipation making it independent of x. Though this does not remove the differences between the magnet temperature cycle within each block, it at least removes the systematic x-dependent thermal drift. 

All spectra were measured on a Bruker DRX 500 spectrometer, at 500.13MHz ( H) and at 125.76MHz ( C). Sample spinning (20Hz) was used for all ID experiments with the exception of the ID NOE and ID ROESY experiments. As is now common, all 2D experiments were performed with the sample static. All experiments were performed at ambient magnet temperature without any special temperature control. 

This nonequilibrium phase diagram is in the form of a cusp in (m,t,h) space (see Ref. 45 for definitions). It is a perfect analogue of a ferromagnetic phase transition if we interpret m,t,h as magnetization, temperature (minus its critical value), and applied magnetic... 

Magnetic measurements, which included magnetization-temperature behavior and particle size determination, were also made on this series of catalysts as a function of reduction treatment. These results, in conjunction with those obtained from kinetic studies, provided a physical picture of the different mechanisms for the niobia and phosphate supports. The same picture is consistent with the less interacting nature of niobia-silica, which should prove useful as a model system for the study of metal-support interactions in general. 

The 7AAP sample showed a normally behaved magnetization-temperature curve after a reduction at 773 K for 1 h. However, an anomalous concave downward curve was observed after a rigorous reduction at 773 K for 16 h (Figure 1). The corresponding Curie temperature (<573 K) is significantly less than that of bulk... 

Figure 1. Magnetization-temperature curves for 7%, Ni/AAP. Reduction treatments were (0) 773K, lh and ( ) 873K, 16h. Dashed line is calculated for a 40 A diameter particle with a Curie temperature of 603 K. (Reproduced with permission from Ref. 14. Copyright 1985, Academic Press, Inc.)...

More recently, increasing interest has been devoted to exploration of multirespon-sive magnetic polymers, which exhibit sensitivity to several external stimuli. Micro- and nanospheres that combine both magnetic, temperature, and pH sensitivity were also elaborated and studied. These new results provide novel possibilities for preparation of more complex magnetic field-responsive materials like membranes with on/off switching control. 

The manufacturers of these lands of instruments all have a long list of appHca-tions. Most of the appHcations are similar and many are pre-packaged as specific analyzers so that they simply unpack, set up and data is acquired within an hour or so after the magnet temperature equilibrates. The instrument vendors for broadline systems are Bruker Instruments [22], Oxford Instruments [23], Praxis [24], Process Control Technology (PCT) [25] and Resonance Instruments [26]. Determination of oil and/or water content dominates the applications. Oil and water analyses are established for seeds and soil in the agriculture industry, catalysts and detergents in the chemicals industry, capsules, tablets and powders in the pharmaceutical and cosmetic industries as well as a wide variety of foodstuffs. 

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