Probe cross coil

Block diagram of a high-resolution NMR spectrometer and the arrangement of the sample in the probe (cross coil configuration). 

Crossed-coil arrangement in a n.m.r. probe, and resolution of the r.f. field (2/f,) into two counter-rotating components H1 and... 

A home-built solid-state NMR spectrometer with stochastic excitation has been described. An overview of the instrument has been given and the control unit and the module for the pulse generation have been described. A static probe with crossed coils for the transmitter and receiver circuits and the data processing part of the spectrometer software have been presented. Several examples of NMR measurements have been shown, including selective excitation in solids and the acquisition of static solid-state NMR spectra with a spectral width of up to 185 kHz. 

It should be noted that very high H homogeneity is necessary only in certain cases. A high resolution spectrum results even if different parts of the sample experience different H s. In a cross coil probe, it is easier to achieve uniform H while having the sample approximate an infinite cylinder with respect to the receiver coil. High H homogeneity is important for multiple pulse experiments, however. 

Crossed coil probes are easy to tune because the transmitter and the receiver functions are independent. Tune the receiver tank circuit for a maximum signal through the receiver from the dip meter. The transmitter coil can be optimized by maximizing the rf field amplitude at the coil as described in the section on transmitter tuning below. 

The extension of their previously developed low temperature method to an 18.8 T system has been described by Lipton et al. A new probe was used with a cross coil and variable capacitors that are operational at cryogenic temperatures. The limitations to sensitivity are discussed, including a new diode network, the utilisation of a cryogenic band pass filter, and the consequences of the RF profiles of the coil. Further, details of the spectroscopy of quadrupolar nuclei in a protein are discussed, such as the observation of the outer transitions and how to distinguish them from the desired 1/2 transition. 

Pyrolysis-Gas Chromatography-Mass Spectrometry. In the experiments, about 2 mg of sample was pyrolyzed at 900°C in flowing helium using a Chemical Data System (CDS) Platinum Coil Pyrolysis Probe controlled by a CDS Model 122 Pyroprobe in normal mode. Products were separated on a 12 meter fused capillary column with a cross-linked poly (dimethylsilicone) stationary phase. The GC column was temperature programmed from -50 to 300°C. Individual compounds were identified with a Hewlett Packard (HP) Model 5995C low resolution quadruple GC/MS System. Data acquisition and reduction were performed on the HP 100 E-series computer running revision E RTE-6/VM software. 

Microscopes. There are two basic modes of operation for X-ray analysis in a modern-day AEMs with a static (or flood) beam and with a rastered beam. This instrument is essentially a conventional TEM with either (a) scanning coils to raster and focus the beam or (b) an extra NminiN (or objective pre-field) condenser lens to provide a small (nm-sized) cross-over of a static beam at the objective plane. Some AEM configurations contain both scanning coils and a third condenser lens whilst others may have only one of these. In either condition, a small-sized electron probe can be obtained as a static or a rastered beam. The basic electron-optical principles which provide nanometer-sized beams for microanalysis are similar to those for electron microdiffraction which are well described by Spence and Carpenter [19]. 

F or the purposes of a discussion related to an experimental spectrometer, it will be assumed that the construction of its probe is based on the common, crossed-coil146 arrangement, in which the static magnetic field (H0) is applied along the z axis, a transmitter coil is oriented... 

After the pulse, the probe acts as the generator of the (small) NMR signal, which enters QHl at port 4 and is funneled with a phase difference of -90° to ports 2 and 3. From there the signal flows, unaffected by the crossed diode packages Dj and Dj (their capacitances are also compensated by coils), to ports 2 and 3 of QH2. Because the phase difference is now -90°, the signal is funneled to port 1 and the preamplifier. 

Particle velocity measurement in multiphase systems can be approximately categorized as invasive (probes, impaction devices) and noninvasive (rings, coils, optical beams). Yan (1996) has further detailed particle velocity measurement according to (1) Doppler methods laser and microwave (2) Cross-correlations methods capacitance, electrodynamic, acoustic or... 

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